Introduction to function calling

Large Language Models (LLMs) are powerful at solving many types of problems. However, they are constrained by the following limitations:

  • They are frozen after training, leading to stale knowledge.
  • They can't query or modify external data.

Function calling can address these shortcomings. Function calling is sometimes referred to as tool use because it allows the model to use external tools such as APIs and functions.

When submitting a prompt to the LLM, you also provide the model with a set of tools that it can use to respond to the user's prompt. For example, you could provide a function get_weather that takes a location parameter and returns information about the weather conditions at that location.

While processing a prompt, the model can choose to delegate certain data processing tasks to the functions that you identify. The model does not call the functions directly. Instead, the model provides structured data output that includes the function to call and parameter values to use. For example, for a prompt What is the weather like in Boston?, the model can delegate processing to the get_weather function and provide the location parameter value Boston, MA.

You can use the structured output from the model to invoke external APIs. For example, you could connect to a weather service API, provide the location Boston, MA, and receive information about temperature, cloud cover, and wind conditions.

You can then provide the API output back to the model, allowing it to complete its response to the prompt. For the weather example, the model may provide the following response: It is currently 38 degrees Fahrenheit in Boston, MA with partly cloudy skies.

Function Calling Interaction 

Supported models

The following models provide support for function calling:

Model Version Function calling launch stage Support for parallel function calling Support for forced function calling
Gemini 1.0 Pro all versions General Availability No No
Gemini 1.5 Flash all versions General Availability Yes Yes
Gemini 1.5 Pro all versions General Availability Yes Yes
Gemini 2.0 Flash all versions Preview Yes Yes

Use cases of function calling

You can use function calling for the following tasks:

Use Case Example description Example link
Integrate with external APIs Get weather information using a meteorological API Notebook tutorial
Convert addresses to latitude/longitude coordinates Notebook tutorial
Convert currencies using a currency exchange API Codelab
Build advanced chatbots Answer customer questions about products and services Notebook tutorial
Create an assistant to answer financial and news questions about companies Notebook tutorial
Structure and control function calls Extract structured entities from raw log data Notebook tutorial
Extract single or multiple parameters from user input Notebook tutorial
Handle lists and nested data structures in function calls Notebook tutorial
Handle function calling behavior Handle parallel function calls and responses Notebook tutorial
Manage when and which functions the model can call Notebook tutorial
Query databases with natural language Convert natural language questions into SQL queries for BigQuery Sample app
Multimodal function calling Use images, videos, audio, and PDFs as input to trigger function calls Notebook tutorial

Here are some more use cases:

  • Interpret voice commands: Create functions that correspond with in-vehicle tasks. For example, you can create functions that turn on the radio or activate the air conditioning. Send audio files of the user's voice commands to the model, and ask the model to convert the audio into text and identify the function that the user wants to call.

  • Automate workflows based on environmental triggers: Create functions to represent processes that can be automated. Provide the model with data from environmental sensors and ask it to parse and process the data to determine whether one or more of the workflows should be activated. For example, a model could process temperature data in a warehouse and choose to activate a sprinkler function.

  • Automate the assignment of support tickets: Provide the model with support tickets, logs, and context-aware rules. Ask the model to process all of this information to determine who the ticket should be assigned to. Call a function to assign the ticket to the person suggested by the model.

  • Retrieve information from a knowledge base: Create functions that retrieve academic articles on a given subject and summarize them. Enable the model to answer questions about academic subjects and provide citations for its answers.

How to create a function calling application

To enable a user to interface with the model and use function calling, you must create code that performs the following tasks:

  1. Set up your environment.
  2. Define and describe a set of available functions using function declarations.
  3. Submit a user's prompt and the function declarations to the model.
  4. Invoke a function using the structured data output from the model.
  5. Provide the function output to the model.

You can create an application that manages all of these tasks. This application can be a text chatbot, a voice agent, an automated workflow, or any other program.

You can use function calling to generate a single text response or to support a chat session. Ad hoc text responses are useful for specific business tasks, including code generation. Chat sessions are useful in freeform, conversational scenarios, where a user is likely to ask follow-up questions.

If you use function calling to generate a single response, you must provide the model with the full context of the interaction. On the other hand, if you use function calling in the context of a chat session, the session stores the context for you and includes it in every model request. In both cases, Vertex AI stores the history of the interaction on the client side.

This guide demonstrates how you can use function calling to generate a single text response. For an end-to-end sample, see Text examples. To learn how to use function calling to support a chat session, see Chat examples.

Step 1: Set up your environment

Import the required modules and initialize the model:

Python 

import vertexai
from vertexai.generative_models import (
    Content,
    FunctionDeclaration,
    GenerationConfig,
    GenerativeModel,
    Part,
    Tool,
)

# Initialize Vertex AI
# TODO(developer): Update and un-comment below lines
# PROJECT_ID = 'your-project-id'
vertexai.init(project=PROJECT_ID, location="us-central1")

# Initialize Gemini model
model = GenerativeModel(model_name="gemini-1.5-flash-002")

Step 2: Declare a set of functions

The application must declare a set of functions that the model can use to process the prompt.

The maximum number of function declarations that can be provided with the request is 128.

You must provide function declarations in a schema format that's compatible with the OpenAPI schema. Vertex AI offers limited support of the OpenAPI schema. The following attributes are supported: type, nullable, required, format, description, properties, items, enum. The following attributes are not supported: default, optional, maximum, oneOf. For best practices related to the function declarations, including tips for names and descriptions, see Best practices.

If you use the REST API, specify the schema using JSON. If you use the Vertex AI SDK for Python, you can specify the schema either manually using a Python dictionary or automatically with the from_func helper function.

JSON 

{
  "contents": ...,
  "tools": [
    {
      "function_declarations": [
        {
          "name": "find_movies",
          "description": "find movie titles currently playing in theaters based on any description, genre, title words, etc.",
          "parameters": {
            "type": "object",
            "properties": {
              "location": {
                "type": "string",
                "description": "The city and state, e.g. San Francisco, CA or a zip code e.g. 95616"
              },
              "description": {
                "type": "string",
                "description": "Any kind of description including category or genre, title words, attributes, etc."
              }
            },
            "required": [
              "description"
            ]
          }
        },
        {
          "name": "find_theaters",
          "description": "find theaters based on location and optionally movie title which are is currently playing in theaters",
          "parameters": {
            "type": "object",
            "properties": {
              "location": {
                "type": "string",
                "description": "The city and state, e.g. San Francisco, CA or a zip code e.g. 95616"
              },
              "movie": {
                "type": "string",
                "description": "Any movie title"
              }
            },
            "required": [
              "location"
            ]
          }
        },
        {
          "name": "get_showtimes",
          "description": "Find the start times for movies playing in a specific theater",
          "parameters": {
            "type": "object",
            "properties": {
              "location": {
                "type": "string",
                "description": "The city and state, e.g. San Francisco, CA or a zip code e.g. 95616"
              },
              "movie": {
                "type": "string",
                "description": "Any movie title"
              },
              "theater": {
                "type": "string",
                "description": "Name of the theater"
              },
              "date": {
                "type": "string",
                "description": "Date for requested showtime"
              }
            },
            "required": [
              "location",
              "movie",
              "theater",
              "date"
            ]
          }
        }
      ]
    }
  ]
}

Python dictionary

The following function declaration takes a single string parameter:

function_name = "get_current_weather"
get_current_weather_func = FunctionDeclaration(
    name=function_name,
    description="Get the current weather in a given location",
    # Function parameters are specified in JSON schema format
    parameters={
        "type": "object",
        "properties": {
            "location": {"type": "string", "description": "The city name of the location for which to get the weather."}
        },
    },
)

The following function declaration takes both object and array parameters:

extract_sale_records_func = FunctionDeclaration(
  name="extract_sale_records",
  description="Extract sale records from a document.",
  parameters={
      "type": "object",
      "properties": {
          "records": {
              "type": "array",
              "description": "A list of sale records",
              "items": {
                  "description": "Data for a sale record",
                  "type": "object",
                  "properties": {
                      "id": {"type": "integer", "description": "The unique id of the sale."},
                      "date": {"type": "string", "description": "Date of the sale, in the format of MMDDYY, e.g., 031023"},
                      "total_amount": {"type": "number", "description": "The total amount of the sale."},
                      "customer_name": {"type": "string", "description": "The name of the customer, including first name and last name."},
                      "customer_contact": {"type": "string", "description": "The phone number of the customer, e.g., 650-123-4567."},
                  },
                  "required": ["id", "date", "total_amount"],
              },
          },
      },
      "required": ["records"],
  },
)

Python from function

The following code sample declares a function that multiplies an array of numbers and uses from_func to generate the FunctionDeclaration schema.

# Define a function. Could be a local function or you can import the requests library to call an API
def multiply_numbers(numbers):
  """
  Calculates the product of all numbers in an array.

  Args:
      numbers: An array of numbers to be multiplied.

  Returns:
      The product of all the numbers. If the array is empty, returns 1.
  """

  if not numbers:  # Handle empty array
      return 1

  product = 1
  for num in numbers:
      product *= num

  return product

multiply_number_func = FunctionDeclaration.from_func(multiply_numbers)

'''
multiply_number_func contains the following schema:

name: "multiply_numbers"
description: "Calculates the product of all numbers in an array."
parameters {
  type_: OBJECT
  properties {
    key: "numbers"
    value {
      description: "An array of numbers to be multiplied."
      title: "Numbers"
    }
  }
  required: "numbers"
  description: "Calculates the product of all numbers in an array."
  title: "multiply_numbers"
}
'''

Step 3: Submit the prompt and function declarations to the model

When the user provides a prompt, the application must provide the model with the user prompt and the function declarations. To configure how the model generates results, the application can provide the model with a generation configuration. To configure how the model uses the function declarations, the application can provide the model with a tool configuration.

Define the user prompt

The following is an example of a user prompt: "What is the weather like in Boston?"

The following is an example of how you can define the user prompt:

Python 

# Define the user's prompt in a Content object that we can reuse in model calls
user_prompt_content = Content(
    role="user",
    parts=[
        Part.from_text("What is the weather like in Boston?"),
    ],
)

For best practices related to the user prompt, see Best practices - User prompt.

Generation configuration

The model can generate different results for different parameter values. The temperature parameter controls the degree of randomness in this generation. Lower temperatures are good for functions that require deterministic parameter values, while higher temperatures are good for functions with parameters that accept more diverse or creative parameter values. A temperature of 0 is deterministic. In this case, responses for a given prompt are mostly deterministic, but a small amount of variation is still possible. To learn more, see Gemini API.

To set this parameter, submit a generation configuration (generation_config) along with the prompt and the function declarations. You can update the temperature parameter during a chat conversation using the Vertex AI API and an updated generation_config. For an example of setting the temperature parameter, see How to submit the prompt and the function declarations.

For best practices related to the generation configuration, see Best practices - Generation configuration.

Tool configuration

You can place some constraints on how the model should use the function declarations that you provide it with. For example, instead of allowing the model to choose between a natural language response and a function call, you can force it to only predict function calls ("forced function calling" or "function calling with controlled generation"). You can also choose to provide the model with a full set of function declarations, but restrict its responses to a subset of these functions.

To place these constraints, submit a tool configuration (tool_config) along with the prompt and the function declarations. In the configuration, you can specify one of the following modes:

Mode Description
AUTO The default model behavior. The model decides whether to predict function calls or a natural language response.
ANY The model is constrained to always predict a function call. If allowed_function_names is not provided, the model picks from all of the available function declarations. If allowed_function_names is provided, the model picks from the set of allowed functions.
NONE The model must not predict function calls. This behaviour is equivalent to a model request without any associated function declarations.

For a list of models that support the ANY mode ("forced function calling"), see supported models.

To learn more, see Function Calling API.

How to submit the prompt and the function declarations

The following is an example of how can you submit the prompt and the function declarations to the model, and constrain the model to predict only get_current_weather function calls.

Python 

# Define a tool that includes some of the functions that we declared earlier
tool = Tool(
    function_declarations=[get_current_weather_func, extract_sale_records_func, multiply_number_func],
)

# Send the prompt and instruct the model to generate content using the Tool object that you just created
response = model.generate_content(
    user_prompt_content,
    generation_config=GenerationConfig(temperature=0),
    tools=[tool],
    tool_config=ToolConfig(
        function_calling_config=ToolConfig.FunctionCallingConfig(
            # ANY mode forces the model to predict only function calls
            mode=ToolConfig.FunctionCallingConfig.Mode.ANY,
            # Allowed function calls to predict when the mode is ANY. If empty, any  of
            # the provided function calls will be predicted.
            allowed_function_names=["get_current_weather"],
        )
    )
)

If the model determines that it needs the output of a particular function, the response that the application receives from the model contains the function name and the parameter values that the function should be called with.

The following is an example of a model response to the user prompt "What is the weather like in Boston?". The model proposes calling the get_current_weather function with the parameter Boston, MA.

candidates {
  content {
    role: "model"
    parts {
      function_call {
        name: "get_current_weather"
        args {
          fields {
            key: "location"
            value {
              string_value: "Boston, MA"
            }
          }
        }
      }
    }
  }
  ...
}

For prompts such as "Get weather details in New Delhi and San Francisco?", the model may propose several parallel function calls. To learn more, see Parallel function calling example.

Step 4: Invoke an external API

If the application receives a function name and parameter values from the model, the application must connect to an external API and call the function.

The following example uses synthetic data to simulate a response payload from an external API:

Python 

# Check the function name that the model responded with, and make an API call to an external system
if (response.candidates[0].function_calls[0].name == "get_current_weather"):
    # Extract the arguments to use in your API call
    location = response.candidates[0].function_calls[0].args["location"]

    # Here you can use your preferred method to make an API request to fetch the current weather, for example:
    # api_response = requests.post(weather_api_url, data={"location": location})

    # In this example, we'll use synthetic data to simulate a response payload from an external API
    api_response = """{ "location": "Boston, MA", "temperature": 38, "description": "Partly Cloudy",
                    "icon": "partly-cloudy", "humidity": 65, "wind": { "speed": 10, "direction": "NW" } }"""

For best practices related to API invocation, see Best practices - API invocation.

Step 5: Provide the function's output to the model

After an application receives a response from an external API, the application must provide this response to the model. The following is an example of how you can do this using Python:

Python 

response = model.generate_content(
    [
        user_prompt_content,  # User prompt
        response.candidates[0].content,  # Function call response
        Content(
            parts=[
                Part.from_function_response(
                    name="get_current_weather",
                    response={
                        "content": api_response,  # Return the API response to Gemini
                    },
                )
            ],
        ),
    ],
    tools=[weather_tool],
)
# Get the model summary response
summary = response.text

If the model had proposed several parallel function calls, the application must provide all of the responses back to the model. To learn more, see Parallel function calling example.

The model may determine that the output of another function is necessary for responding to the prompt. In this case, the response that the application receives from the model contains another function name and another set of parameter values.

If the model determines that the API response is sufficient for responding to the user's prompt, it creates a natural language response and returns it to the application. In this case, the application must pass the response back to the user. The following is an example of a response:

It is currently 38 degrees Fahrenheit in Boston, MA with partly cloudy skies. The humidity is 65% and the wind is blowing at 10 mph from the northwest.

Examples of function calling

Text examples

You can use function calling to generate a single text response. Ad hoc text responses are useful for specific business tasks, including code generation.

If you use function calling to generate a single response, you must provide the model with the full context of the interaction. Vertex AI stores the history of the interaction on the client side.

Python

This example demonstrates a text scenario with one function and one prompt. It uses the GenerativeModel class and its methods. For more information about using the Vertex AI SDK for Python with Gemini multimodal models, see Introduction to multimodal classes in the Vertex AI SDK for Python.

Python

To learn how to install or update the Vertex AI SDK for Python, see Install the Vertex AI SDK for Python. For more information, see the Python API reference documentation. 

import vertexai

from vertexai.generative_models import (
    Content,
    FunctionDeclaration,
    GenerationConfig,
    GenerativeModel,
    Part,
    Tool,
)

# TODO(developer): Update & uncomment below line
# PROJECT_ID = "your-project-id"

# Initialize Vertex AI
vertexai.init(project=PROJECT_ID, location="us-central1")

# Initialize Gemini model
model = GenerativeModel("gemini-1.5-flash-002")

# Define the user's prompt in a Content object that we can reuse in model calls
user_prompt_content = Content(
    role="user",
    parts=[
        Part.from_text("What is the weather like in Boston?"),
    ],
)

# Specify a function declaration and parameters for an API request
function_name = "get_current_weather"
get_current_weather_func = FunctionDeclaration(
    name=function_name,
    description="Get the current weather in a given location",
    # Function parameters are specified in JSON schema format
    parameters={
        "type": "object",
        "properties": {"location": {"type": "string", "description": "Location"}},
    },
)

# Define a tool that includes the above get_current_weather_func
weather_tool = Tool(
    function_declarations=[get_current_weather_func],
)

# Send the prompt and instruct the model to generate content using the Tool that you just created
response = model.generate_content(
    user_prompt_content,
    generation_config=GenerationConfig(temperature=0),
    tools=[weather_tool],
)
function_call = response.candidates[0].function_calls[0]
print(function_call)

# Check the function name that the model responded with, and make an API call to an external system
if function_call.name == function_name:
    # Extract the arguments to use in your API call
    location = function_call.args["location"]  # noqa: F841

    # Here you can use your preferred method to make an API request to fetch the current weather, for example:
    # api_response = requests.post(weather_api_url, data={"location": location})

    # In this example, we'll use synthetic data to simulate a response payload from an external API
    api_response = """{ "location": "Boston, MA", "temperature": 38, "description": "Partly Cloudy",
                    "icon": "partly-cloudy", "humidity": 65, "wind": { "speed": 10, "direction": "NW" } }"""

# Return the API response to Gemini so it can generate a model response or request another function call
response = model.generate_content(
    [
        user_prompt_content,  # User prompt
        response.candidates[0].content,  # Function call response
        Content(
            parts=[
                Part.from_function_response(
                    name=function_name,
                    response={
                        "content": api_response,  # Return the API response to Gemini
                    },
                ),
            ],
        ),
    ],
    tools=[weather_tool],
)

# Get the model response
print(response.text)
# Example response:
# The weather in Boston is partly cloudy with a temperature of 38 degrees Fahrenheit.
# The humidity is 65% and the wind is blowing from the northwest at 10 mph.

Node.js

This example demonstrates a text scenario with one function and one prompt.

Node.js

Before trying this sample, follow the Node.js setup instructions in the Vertex AI quickstart using client libraries. For more information, see the Vertex AI Node.js API reference documentation.

To authenticate to Vertex AI, set up Application Default Credentials. For more information, see Set up authentication for a local development environment. 

const {
  VertexAI,
  FunctionDeclarationSchemaType,
} = require('@google-cloud/vertexai');

const functionDeclarations = [
  {
    function_declarations: [
      {
        name: 'get_current_weather',
        description: 'get weather in a given location',
        parameters: {
          type: FunctionDeclarationSchemaType.OBJECT,
          properties: {
            location: {type: FunctionDeclarationSchemaType.STRING},
            unit: {
              type: FunctionDeclarationSchemaType.STRING,
              enum: ['celsius', 'fahrenheit'],
            },
          },
          required: ['location'],
        },
      },
    ],
  },
];

const functionResponseParts = [
  {
    functionResponse: {
      name: 'get_current_weather',
      response: {name: 'get_current_weather', content: {weather: 'super nice'}},
    },
  },
];

/**
 * TODO(developer): Update these variables before running the sample.
 */
async function functionCallingStreamContent(
  projectId = 'PROJECT_ID',
  location = 'us-central1',
  model = 'gemini-1.5-flash-001'
) {
  // Initialize Vertex with your Cloud project and location
  const vertexAI = new VertexAI({project: projectId, location: location});

  // Instantiate the model
  const generativeModel = vertexAI.getGenerativeModel({
    model: model,
  });

  const request = {
    contents: [
      {role: 'user', parts: [{text: 'What is the weather in Boston?'}]},
      {
        role: 'ASSISTANT',
        parts: [
          {
            functionCall: {
              name: 'get_current_weather',
              args: {location: 'Boston'},
            },
          },
        ],
      },
      {role: 'USER', parts: functionResponseParts},
    ],
    tools: functionDeclarations,
  };
  const streamingResp = await generativeModel.generateContentStream(request);
  for await (const item of streamingResp.stream) {
    console.log(item.candidates[0].content.parts[0].text);
  }
}

Go

This example demonstrates a text scenario with one function and one prompt.

Go

Before trying this sample, follow the Go setup instructions in the Vertex AI quickstart using client libraries. For more information, see the Vertex AI Go API reference documentation.

To authenticate to Vertex AI, set up Application Default Credentials. For more information, see Set up authentication for a local development environment. 

import (
	"context"
	"encoding/json"
	"errors"
	"fmt"
	"io"

	"cloud.google.com/go/vertexai/genai"
)

// functionCalling demonstrates how to submit a prompt and a function declaration to the model,
// allowing it to suggest a call to the function to fetch external data. Returning this data
// to the model enables it to generate a text response that incorporates the data.
func functionCalling(w io.Writer, projectID, location, modelName string) error {
	// location = "us-central1"
	// modelName = "gemini-1.5-flash-002"
	ctx := context.Background()
	client, err := genai.NewClient(ctx, projectID, location)
	if err != nil {
		return fmt.Errorf("failed to create GenAI client: %w", err)
	}
	defer client.Close()

	model := client.GenerativeModel(modelName)
	// Set temperature to 0.0 for maximum determinism in function calling.
	model.SetTemperature(0.0)

	funcName := "getCurrentWeather"
	funcDecl := &genai.FunctionDeclaration{
		Name:        funcName,
		Description: "Get the current weather in a given location",
		Parameters: &genai.Schema{
			Type: genai.TypeObject,
			Properties: map[string]*genai.Schema{
				"location": {
					Type:        genai.TypeString,
					Description: "location",
				},
			},
			Required: []string{"location"},
		},
	}
	// Add the weather function to our model toolbox.
	model.Tools = []*genai.Tool{
		{
			FunctionDeclarations: []*genai.FunctionDeclaration{funcDecl},
		},
	}

	prompt := genai.Text("What's the weather like in Boston?")
	resp, err := model.GenerateContent(ctx, prompt)

	if err != nil {
		return fmt.Errorf("failed to generate content: %w", err)
	}
	if len(resp.Candidates) == 0 {
		return errors.New("got empty response from model")
	} else if len(resp.Candidates[0].FunctionCalls()) == 0 {
		return errors.New("got no function call suggestions from model")
	}

	// In a production environment, consider adding validations for function names and arguments.
	for _, fnCall := range resp.Candidates[0].FunctionCalls() {
		fmt.Fprintf(w, "The model suggests to call the function %q with args: %v\n", fnCall.Name, fnCall.Args)
		// Example response:
		// The model suggests to call the function "getCurrentWeather" with args: map[location:Boston]
	}
	// Use synthetic data to simulate a response from the external API.
	// In a real application, this would come from an actual weather API.
	mockAPIResp, err := json.Marshal(map[string]string{
		"location":         "Boston",
		"temperature":      "38",
		"temperature_unit": "F",
		"description":      "Cold and cloudy",
		"humidity":         "65",
		"wind":             `{"speed": "10", "direction": "NW"}`,
	})
	if err != nil {
		return fmt.Errorf("failed to marshal function response to JSON: %w", err)
	}

	funcResp := &genai.FunctionResponse{
		Name: funcName,
		Response: map[string]any{
			"content": mockAPIResp,
		},
	}

	// Return the API response to the model allowing it to complete its response.
	resp, err = model.GenerateContent(ctx, prompt, funcResp)
	if err != nil {
		return fmt.Errorf("failed to generate content: %w", err)
	}
	if len(resp.Candidates) == 0 || len(resp.Candidates[0].Content.Parts) == 0 {
		return errors.New("got empty response from model")
	}

	fmt.Fprintln(w, resp.Candidates[0].Content.Parts[0])
	// Example response:
	// The weather in Boston is cold and cloudy, with a humidity of 65% and a temperature of 38°F. ...

	return nil
}

C#

This example demonstrates a text scenario with one function and one prompt.

C#

Before trying this sample, follow the C# setup instructions in the Vertex AI quickstart using client libraries. For more information, see the Vertex AI C# API reference documentation.

To authenticate to Vertex AI, set up Application Default Credentials. For more information, see Set up authentication for a local development environment. 


using Google.Cloud.AIPlatform.V1;
using System;
using System.Threading.Tasks;
using Type = Google.Cloud.AIPlatform.V1.Type;
using Value = Google.Protobuf.WellKnownTypes.Value;

public class FunctionCalling
{
    public async Task<string> GenerateFunctionCall(
        string projectId = "your-project-id",
        string location = "us-central1",
        string publisher = "google",
        string model = "gemini-1.5-flash-001")
    {
        var predictionServiceClient = new PredictionServiceClientBuilder
        {
            Endpoint = $"{location}-aiplatform.googleapis.com"
        }.Build();

        // Define the user's prompt in a Content object that we can reuse in
        // model calls
        var userPromptContent = new Content
        {
            Role = "USER",
            Parts =
            {
                new Part { Text = "What is the weather like in Boston?" }
            }
        };

        // Specify a function declaration and parameters for an API request
        var functionName = "get_current_weather";
        var getCurrentWeatherFunc = new FunctionDeclaration
        {
            Name = functionName,
            Description = "Get the current weather in a given location",
            Parameters = new OpenApiSchema
            {
                Type = Type.Object,
                Properties =
                {
                    ["location"] = new()
                    {
                        Type = Type.String,
                        Description = "Get the current weather in a given location"
                    },
                    ["unit"] = new()
                    {
                        Type = Type.String,
                        Description = "The unit of measurement for the temperature",
                        Enum = {"celsius", "fahrenheit"}
                    }
                },
                Required = { "location" }
            }
        };

        // Send the prompt and instruct the model to generate content using the tool that you just created
        var generateContentRequest = new GenerateContentRequest
        {
            Model = $"projects/{projectId}/locations/{location}/publishers/{publisher}/models/{model}",
            GenerationConfig = new GenerationConfig
            {
                Temperature = 0f
            },
            Contents =
            {
                userPromptContent
            },
            Tools =
            {
                new Tool
                {
                    FunctionDeclarations = { getCurrentWeatherFunc }
                }
            }
        };

        GenerateContentResponse response = await predictionServiceClient.GenerateContentAsync(generateContentRequest);

        var functionCall = response.Candidates[0].Content.Parts[0].FunctionCall;
        Console.WriteLine(functionCall);

        string apiResponse = "";

        // Check the function name that the model responded with, and make an API call to an external system
        if (functionCall.Name == functionName)
        {
            // Extract the arguments to use in your API call
            string locationCity = functionCall.Args.Fields["location"].StringValue;

            // Here you can use your preferred method to make an API request to
            // fetch the current weather

            // In this example, we'll use synthetic data to simulate a response
            // payload from an external API
            apiResponse = @"{ ""location"": ""Boston, MA"",
                    ""temperature"": 38, ""description"": ""Partly Cloudy""}";
        }

        // Return the API response to Gemini so it can generate a model response or request another function call
        generateContentRequest = new GenerateContentRequest
        {
            Model = $"projects/{projectId}/locations/{location}/publishers/{publisher}/models/{model}",
            Contents =
            {
                userPromptContent, // User prompt
                response.Candidates[0].Content, // Function call response,
                new Content
                {
                    Parts =
                    {
                        new Part
                        {
                            FunctionResponse = new()
                            {
                                Name = functionName,
                                Response = new()
                                {
                                    Fields =
                                    {
                                        { "content", new Value { StringValue = apiResponse } }
                                    }
                                }
                            }
                        }
                    }
                }
            },
            Tools =
            {
                new Tool
                {
                    FunctionDeclarations = { getCurrentWeatherFunc }
                }
            }
        };

        response = await predictionServiceClient.GenerateContentAsync(generateContentRequest);

        string responseText = response.Candidates[0].Content.Parts[0].Text;
        Console.WriteLine(responseText);

        return responseText;
    }
}

REST

This example demonstrates a text scenario with three functions and one prompt.

In this example, you call the generative AI model twice.

  • In the first call, you provide the model with the prompt and the function declarations.
  • In the second call, you provide the model with the API response.

First model request

The request must define a prompt in the text parameter. This example defines the following prompt: "Which theaters in Mountain View show the Barbie movie?".

The request must also define a tool (tools) with a set of function declarations (functionDeclarations). These function declarations must be specified in a format that's compatible with the OpenAPI schema. This example defines the following functions:

  • find_movies finds movie titles playing in theaters.
  • find_theatres finds theaters based on location.
  • get_showtimes finds the start times for movies playing in a specific theater.

To learn more about the parameters of the model request, see Gemini API.

Replace my-project with the name of your Google Cloud project.

First model request

PROJECT_ID=my-project
MODEL_ID=gemini-1.0-pro
API=streamGenerateContent
curl -X POST -H "Authorization: Bearer $(gcloud auth print-access-token)" -H "Content-Type: application/json"  https://us-central1-aiplatform.googleapis.com/v1/projects/${PROJECT_ID}/locations/us-central1/publishers/google/models/${MODEL_ID}:${API} -d '{
"contents": {
  "role": "user",
  "parts": {
    "text": "Which theaters in Mountain View show the Barbie movie?"
  }
},
"tools": [
  {
    "function_declarations": [
      {
        "name": "find_movies",
        "description": "find movie titles currently playing in theaters based on any description, genre, title words, etc.",
        "parameters": {
          "type": "object",
          "properties": {
            "location": {
              "type": "string",
              "description": "The city and state, e.g. San Francisco, CA or a zip code e.g. 95616"
            },
            "description": {
              "type": "string",
              "description": "Any kind of description including category or genre, title words, attributes, etc."
            }
          },
          "required": [
            "description"
          ]
        }
      },
      {
        "name": "find_theaters",
        "description": "find theaters based on location and optionally movie title which are is currently playing in theaters",
        "parameters": {
          "type": "object",
          "properties": {
            "location": {
              "type": "string",
              "description": "The city and state, e.g. San Francisco, CA or a zip code e.g. 95616"
            },
            "movie": {
              "type": "string",
              "description": "Any movie title"
            }
          },
          "required": [
            "location"
          ]
        }
      },
      {
        "name": "get_showtimes",
        "description": "Find the start times for movies playing in a specific theater",
        "parameters": {
          "type": "object",
          "properties": {
            "location": {
              "type": "string",
              "description": "The city and state, e.g. San Francisco, CA or a zip code e.g. 95616"
            },
            "movie": {
              "type": "string",
              "description": "Any movie title"
            },
            "theater": {
              "type": "string",
              "description": "Name of the theater"
            },
            "date": {
              "type": "string",
              "description": "Date for requested showtime"
            }
          },
          "required": [
            "location",
            "movie",
            "theater",
            "date"
          ]
        }
      }
    ]
  }
]
}'

For the prompt "Which theaters in Mountain View show the Barbie movie?", the model might return the function find_theatres with parameters Barbie and Mountain View, CA.

Response to first model request

[{
"candidates": [
  {
    "content": {
      "parts": [
        {
          "functionCall": {
            "name": "find_theaters",
            "args": {
              "movie": "Barbie",
              "location": "Mountain View, CA"
            }
          }
        }
      ]
    },
    "finishReason": "STOP",
    "safetyRatings": [
      {
        "category": "HARM_CATEGORY_HARASSMENT",
        "probability": "NEGLIGIBLE"
      },
      {
        "category": "HARM_CATEGORY_HATE_SPEECH",
        "probability": "NEGLIGIBLE"
      },
      {
        "category": "HARM_CATEGORY_SEXUALLY_EXPLICIT",
        "probability": "NEGLIGIBLE"
      },
      {
        "category": "HARM_CATEGORY_DANGEROUS_CONTENT",
        "probability": "NEGLIGIBLE"
      }
    ]
  }
],
"usageMetadata": {
  "promptTokenCount": 9,
  "totalTokenCount": 9
}
}]

Second model request

This example uses synthetic data instead of calling the external API. There are two results, each with two parameters (name and address):

  1. name: AMC Mountain View 16, address: 2000 W El Camino Real, Mountain View, CA 94040
  2. name: Regal Edwards 14, address: 245 Castro St, Mountain View, CA 94040

Replace my-project with the name of your Google Cloud project.

Second model request

PROJECT_ID=my-project
MODEL_ID=gemini-1.0-pro
API=streamGenerateContent
curl -X POST -H "Authorization: Bearer $(gcloud auth print-access-token)" -H "Content-Type: application/json"  https://us-central1-aiplatform.googleapis.com/v1/projects/${PROJECT_ID}/locations/us-central1/publishers/google/models/${MODEL_ID}:${API} -d '{
"contents": [{
  "role": "user",
  "parts": [{
    "text": "Which theaters in Mountain View show the Barbie movie?"
  }]
}, {
  "role": "model",
  "parts": [{
    "functionCall": {
      "name": "find_theaters",
      "args": {
        "location": "Mountain View, CA",
        "movie": "Barbie"
      }
    }
  }]
}, {
  "parts": [{
    "functionResponse": {
      "name": "find_theaters",
      "response": {
        "name": "find_theaters",
        "content": {
          "movie": "Barbie",
          "theaters": [{
            "name": "AMC Mountain View 16",
            "address": "2000 W El Camino Real, Mountain View, CA 94040"
          }, {
            "name": "Regal Edwards 14",
            "address": "245 Castro St, Mountain View, CA 94040"
          }]
        }
      }
    }
  }]
}],
"tools": [{
  "functionDeclarations": [{
    "name": "find_movies",
    "description": "find movie titles currently playing in theaters based on any description, genre, title words, etc.",
    "parameters": {
      "type": "OBJECT",
      "properties": {
        "location": {
          "type": "STRING",
          "description": "The city and state, e.g. San Francisco, CA or a zip code e.g. 95616"
        },
        "description": {
          "type": "STRING",
          "description": "Any kind of description including category or genre, title words, attributes, etc."
        }
      },
      "required": ["description"]
    }
  }, {
    "name": "find_theaters",
    "description": "find theaters based on location and optionally movie title which are is currently playing in theaters",
    "parameters": {
      "type": "OBJECT",
      "properties": {
        "location": {
          "type": "STRING",
          "description": "The city and state, e.g. San Francisco, CA or a zip code e.g. 95616"
        },
        "movie": {
          "type": "STRING",
          "description": "Any movie title"
        }
      },
      "required": ["location"]
    }
  }, {
    "name": "get_showtimes",
    "description": "Find the start times for movies playing in a specific theater",
    "parameters": {
      "type": "OBJECT",
      "properties": {
        "location": {
          "type": "STRING",
          "description": "The city and state, e.g. San Francisco, CA or a zip code e.g. 95616"
        },
        "movie": {
          "type": "STRING",
          "description": "Any movie title"
        },
        "theater": {
          "type": "STRING",
          "description": "Name of the theater"
        },
        "date": {
          "type": "STRING",
          "description": "Date for requested showtime"
        }
      },
      "required": ["location", "movie", "theater", "date"]
    }
  }]
}]
}'

The model's response might be similar to the following:

Response to second model request

{
"candidates": [
  {
    "content": {
      "parts": [
        {
          "text": " OK. Barbie is showing in two theaters in Mountain View, CA: AMC Mountain View 16 and Regal Edwards 14."
        }
      ]
    }
  }
],
"usageMetadata": {
  "promptTokenCount": 9,
  "candidatesTokenCount": 27,
  "totalTokenCount": 36
}
}

Chat examples

You can use function calling to support a chat session. Chat sessions are useful in freeform, conversational scenarios, where a user is likely to ask follow-up questions.

If you use function calling in the context of a chat session, the session stores the context for you and includes it in every model request. Vertex AI stores the history of the interaction on the client side.

Python

This example demonstrates a chat scenario with two functions and two sequential prompts. It uses the GenerativeModel class and its methods. For more information about using the Vertex AI SDK for Python with multimodal models, see Introduction to multimodal classes in the Vertex AI SDK for Python.

To learn how to install or update Python, see Install the Vertex AI SDK for Python. For more information, see the Python API reference documentation.

import vertexai

from vertexai.generative_models import (
    FunctionDeclaration,
    GenerationConfig,
    GenerativeModel,
    Part,
    Tool,
)

# TODO(developer): Update & uncomment below line
# PROJECT_ID = "your-project-id"

# Initialize Vertex AI
vertexai.init(project=PROJECT_ID, location="us-central1")

# Specify a function declaration and parameters for an API request
get_product_sku = "get_product_sku"
get_product_sku_func = FunctionDeclaration(
    name=get_product_sku,
    description="Get the SKU for a product",
    # Function parameters are specified in OpenAPI JSON schema format
    parameters={
        "type": "object",
        "properties": {
            "product_name": {"type": "string", "description": "Product name"}
        },
    },
)

# Specify another function declaration and parameters for an API request
get_store_location_func = FunctionDeclaration(
    name="get_store_location",
    description="Get the location of the closest store",
    # Function parameters are specified in JSON schema format
    parameters={
        "type": "object",
        "properties": {"location": {"type": "string", "description": "Location"}},
    },
)

# Define a tool that includes the above functions
retail_tool = Tool(
    function_declarations=[
        get_product_sku_func,
        get_store_location_func,
    ],
)

# Initialize Gemini model
model = GenerativeModel(
    model_name="gemini-1.5-flash-001",
    generation_config=GenerationConfig(temperature=0),
    tools=[retail_tool],
)

# Start a chat session
chat = model.start_chat()

# Send a prompt for the first conversation turn that should invoke the get_product_sku function
response = chat.send_message("Do you have the Pixel 8 Pro in stock?")

function_call = response.candidates[0].function_calls[0]
print(function_call)

# Check the function name that the model responded with, and make an API call to an external system
if function_call.name == get_product_sku:
    # Extract the arguments to use in your API call
    product_name = function_call.args["product_name"]  # noqa: F841

    # Here you can use your preferred method to make an API request to retrieve the product SKU, as in:
    # api_response = requests.post(product_api_url, data={"product_name": product_name})

    # In this example, we'll use synthetic data to simulate a response payload from an external API
    api_response = {"sku": "GA04834-US", "in_stock": "Yes"}

# Return the API response to Gemini, so it can generate a model response or request another function call
response = chat.send_message(
    Part.from_function_response(
        name=get_product_sku,
        response={
            "content": api_response,
        },
    ),
)
# Extract the text from the model response
print(response.text)

# Send a prompt for the second conversation turn that should invoke the get_store_location function
response = chat.send_message(
    "Is there a store in Mountain View, CA that I can visit to try it out?"
)

function_call = response.candidates[0].function_calls[0]
print(function_call)

# Check the function name that the model responded with, and make an API call to an external system
if function_call.name == "get_store_location":
    # Extract the arguments to use in your API call
    location = function_call.args["location"]  # noqa: F841

    # Here you can use your preferred method to make an API request to retrieve store location closest to the user, as in:
    # api_response = requests.post(store_api_url, data={"location": location})

    # In this example, we'll use synthetic data to simulate a response payload from an external API
    api_response = {"store": "2000 N Shoreline Blvd, Mountain View, CA 94043, US"}

# Return the API response to Gemini, so it can generate a model response or request another function call
response = chat.send_message(
    Part.from_function_response(
        name="get_store_location",
        response={
            "content": api_response,
        },
    ),
)

# Extract the text from the model response
print(response.text)
# Example response:
# name: "get_product_sku"
# args {
#   fields { key: "product_name" value {string_value: "Pixel 8 Pro" }
#   }
# }
# Yes, we have the Pixel 8 Pro in stock.
# name: "get_store_location"
# args {
#   fields { key: "location" value { string_value: "Mountain View, CA" }
#   }
# }
# Yes, there is a store located at 2000 N Shoreline Blvd, Mountain View, CA 94043, US.

Java

Before trying this sample, follow the Java setup instructions in the Vertex AI quickstart using client libraries. For more information, see the Vertex AI Java API reference documentation.

To authenticate to Vertex AI, set up Application Default Credentials. For more information, see Set up authentication for a local development environment. 

import com.google.cloud.vertexai.VertexAI;
import com.google.cloud.vertexai.api.Content;
import com.google.cloud.vertexai.api.FunctionDeclaration;
import com.google.cloud.vertexai.api.GenerateContentResponse;
import com.google.cloud.vertexai.api.Schema;
import com.google.cloud.vertexai.api.Tool;
import com.google.cloud.vertexai.api.Type;
import com.google.cloud.vertexai.generativeai.ChatSession;
import com.google.cloud.vertexai.generativeai.ContentMaker;
import com.google.cloud.vertexai.generativeai.GenerativeModel;
import com.google.cloud.vertexai.generativeai.PartMaker;
import com.google.cloud.vertexai.generativeai.ResponseHandler;
import java.io.IOException;
import java.util.Arrays;
import java.util.Collections;

public class FunctionCalling {
  public static void main(String[] args) throws IOException {
    // TODO(developer): Replace these variables before running the sample.
    String projectId = "your-google-cloud-project-id";
    String location = "us-central1";
    String modelName = "gemini-1.5-flash-001";

    String promptText = "What's the weather like in Paris?";

    whatsTheWeatherLike(projectId, location, modelName, promptText);
  }

  // A request involving the interaction with an external tool
  public static String whatsTheWeatherLike(String projectId, String location,
                                           String modelName, String promptText)
      throws IOException {
    // Initialize client that will be used to send requests.
    // This client only needs to be created once, and can be reused for multiple requests.
    try (VertexAI vertexAI = new VertexAI(projectId, location)) {

      FunctionDeclaration functionDeclaration = FunctionDeclaration.newBuilder()
          .setName("getCurrentWeather")
          .setDescription("Get the current weather in a given location")
          .setParameters(
              Schema.newBuilder()
                  .setType(Type.OBJECT)
                  .putProperties("location", Schema.newBuilder()
                      .setType(Type.STRING)
                      .setDescription("location")
                      .build()
                  )
                  .addRequired("location")
                  .build()
          )
          .build();

      System.out.println("Function declaration:");
      System.out.println(functionDeclaration);

      // Add the function to a "tool"
      Tool tool = Tool.newBuilder()
          .addFunctionDeclarations(functionDeclaration)
          .build();

      // Start a chat session from a model, with the use of the declared function.
      GenerativeModel model = new GenerativeModel(modelName, vertexAI)
          .withTools(Arrays.asList(tool));
      ChatSession chat = model.startChat();

      System.out.println(String.format("Ask the question: %s", promptText));
      GenerateContentResponse response = chat.sendMessage(promptText);

      // The model will most likely return a function call to the declared
      // function `getCurrentWeather` with "Paris" as the value for the
      // argument `location`.
      System.out.println("\nPrint response: ");
      System.out.println(ResponseHandler.getContent(response));

      // Provide an answer to the model so that it knows what the result
      // of a "function call" is.
      Content content =
          ContentMaker.fromMultiModalData(
              PartMaker.fromFunctionResponse(
                  "getCurrentWeather",
                  Collections.singletonMap("currentWeather", "sunny")));
      System.out.println("Provide the function response: ");
      System.out.println(content);
      response = chat.sendMessage(content);

      // See what the model replies now
      System.out.println("Print response: ");
      String finalAnswer = ResponseHandler.getText(response);
      System.out.println(finalAnswer);

      return finalAnswer;
    }
  }
}

Go

Before trying this sample, follow the Go setup instructions in the Vertex AI quickstart using client libraries. For more information, see the Vertex AI Go API reference documentation.

To authenticate to Vertex AI, set up Application Default Credentials. For more information, see Set up authentication for a local development environment. 

import (
	"context"
	"encoding/json"
	"errors"
	"fmt"
	"io"

	"cloud.google.com/go/vertexai/genai"
)

// functionCallsChat opens a chat session and sends 4 messages to the model:
// - convert a first text question into a structured function call request
// - convert the first structured function call response into natural language
// - convert a second text question into a structured function call request
// - convert the second structured function call response into natural language
func functionCallsChat(w io.Writer, projectID, location, modelName string) error {
	// location := "us-central1"
	// modelName := "gemini-1.5-flash-001"
	ctx := context.Background()
	client, err := genai.NewClient(ctx, projectID, location)
	if err != nil {
		return fmt.Errorf("unable to create client: %w", err)
	}
	defer client.Close()

	model := client.GenerativeModel(modelName)

	// Build an OpenAPI schema, in memory
	paramsProduct := &genai.Schema{
		Type: genai.TypeObject,
		Properties: map[string]*genai.Schema{
			"productName": {
				Type:        genai.TypeString,
				Description: "Product name",
			},
		},
	}
	fundeclProductInfo := &genai.FunctionDeclaration{
		Name:        "getProductSku",
		Description: "Get the SKU for a product",
		Parameters:  paramsProduct,
	}
	paramsStore := &genai.Schema{
		Type: genai.TypeObject,
		Properties: map[string]*genai.Schema{
			"location": {
				Type:        genai.TypeString,
				Description: "Location",
			},
		},
	}
	fundeclStoreLocation := &genai.FunctionDeclaration{
		Name:        "getStoreLocation",
		Description: "Get the location of the closest store",
		Parameters:  paramsStore,
	}
	model.Tools = []*genai.Tool{
		{FunctionDeclarations: []*genai.FunctionDeclaration{
			fundeclProductInfo,
			fundeclStoreLocation,
		}},
	}
	model.SetTemperature(0.0)

	chat := model.StartChat()

	// Send a prompt for the first conversation turn that should invoke the getProductSku function
	prompt := "Do you have the Pixel 8 Pro in stock?"
	fmt.Fprintf(w, "Question: %s\n", prompt)
	resp, err := chat.SendMessage(ctx, genai.Text(prompt))
	if err != nil {
		return err
	}
	if len(resp.Candidates) == 0 ||
		len(resp.Candidates[0].Content.Parts) == 0 {
		return errors.New("empty response from model")
	}

	// The model has returned a function call to the declared function `getProductSku`
	// with a value for the argument `productName`.
	jsondata, err := json.MarshalIndent(resp.Candidates[0].Content.Parts[0], "\t", "  ")
	if err != nil {
		return fmt.Errorf("json.MarshalIndent: %w", err)
	}
	fmt.Fprintf(w, "function call generated by the model:\n\t%s\n", string(jsondata))

	// Create a function call response, to simulate the result of a call to a
	// real service
	funresp := &genai.FunctionResponse{
		Name: "getProductSku",
		Response: map[string]any{
			"sku":      "GA04834-US",
			"in_stock": "yes",
		},
	}
	jsondata, err = json.MarshalIndent(funresp, "\t", "  ")
	if err != nil {
		return fmt.Errorf("json.MarshalIndent: %w", err)
	}
	fmt.Fprintf(w, "function call response sent to the model:\n\t%s\n\n", string(jsondata))

	// And provide the function call response to the model
	resp, err = chat.SendMessage(ctx, funresp)
	if err != nil {
		return err
	}
	if len(resp.Candidates) == 0 ||
		len(resp.Candidates[0].Content.Parts) == 0 {
		return errors.New("empty response from model")
	}

	// The model has taken the function call response as input, and has
	// reformulated the response to the user.
	jsondata, err = json.MarshalIndent(resp.Candidates[0].Content.Parts[0], "\t", "  ")
	if err != nil {
		return fmt.Errorf("json.MarshalIndent: %w", err)
	}
	fmt.Fprintf(w, "Answer generated by the model:\n\t%s\n\n", string(jsondata))

	// Send a prompt for the second conversation turn that should invoke the getStoreLocation function
	prompt2 := "Is there a store in Mountain View, CA that I can visit to try it out?"
	fmt.Fprintf(w, "Question: %s\n", prompt)

	resp, err = chat.SendMessage(ctx, genai.Text(prompt2))
	if err != nil {
		return err
	}
	if len(resp.Candidates) == 0 ||
		len(resp.Candidates[0].Content.Parts) == 0 {
		return errors.New("empty response from model")
	}

	// The model has returned a function call to the declared function `getStoreLocation`
	// with a value for the argument `store`.
	jsondata, err = json.MarshalIndent(resp.Candidates[0].Content.Parts[0], "\t", "  ")
	if err != nil {
		return fmt.Errorf("json.MarshalIndent: %w", err)
	}
	fmt.Fprintf(w, "function call generated by the model:\n\t%s\n", string(jsondata))

	// Create a function call response, to simulate the result of a call to a
	// real service
	funresp = &genai.FunctionResponse{
		Name: "getStoreLocation",
		Response: map[string]any{
			"store": "2000 N Shoreline Blvd, Mountain View, CA 94043, US",
		},
	}
	jsondata, err = json.MarshalIndent(funresp, "\t", "  ")
	if err != nil {
		return fmt.Errorf("json.MarshalIndent: %w", err)
	}
	fmt.Fprintf(w, "function call response sent to the model:\n\t%s\n\n", string(jsondata))

	// And provide the function call response to the model
	resp, err = chat.SendMessage(ctx, funresp)
	if err != nil {
		return err
	}
	if len(resp.Candidates) == 0 ||
		len(resp.Candidates[0].Content.Parts) == 0 {
		return errors.New("empty response from model")
	}

	// The model has taken the function call response as input, and has
	// reformulated the response to the user.
	jsondata, err = json.MarshalIndent(resp.Candidates[0].Content.Parts[0], "\t", "  ")
	if err != nil {
		return fmt.Errorf("json.MarshalIndent: %w", err)
	}
	fmt.Fprintf(w, "Answer generated by the model:\n\t%s\n\n", string(jsondata))
	return nil
}

Node.js

Before trying this sample, follow the Node.js setup instructions in the Vertex AI quickstart using client libraries. For more information, see the Vertex AI Node.js API reference documentation.

To authenticate to Vertex AI, set up Application Default Credentials. For more information, see Set up authentication for a local development environment. 

const {
  VertexAI,
  FunctionDeclarationSchemaType,
} = require('@google-cloud/vertexai');

const functionDeclarations = [
  {
    function_declarations: [
      {
        name: 'get_current_weather',
        description: 'get weather in a given location',
        parameters: {
          type: FunctionDeclarationSchemaType.OBJECT,
          properties: {
            location: {type: FunctionDeclarationSchemaType.STRING},
            unit: {
              type: FunctionDeclarationSchemaType.STRING,
              enum: ['celsius', 'fahrenheit'],
            },
          },
          required: ['location'],
        },
      },
    ],
  },
];

const functionResponseParts = [
  {
    functionResponse: {
      name: 'get_current_weather',
      response: {name: 'get_current_weather', content: {weather: 'super nice'}},
    },
  },
];

/**
 * TODO(developer): Update these variables before running the sample.
 */
async function functionCallingStreamChat(
  projectId = 'PROJECT_ID',
  location = 'us-central1',
  model = 'gemini-1.5-flash-001'
) {
  // Initialize Vertex with your Cloud project and location
  const vertexAI = new VertexAI({project: projectId, location: location});

  // Instantiate the model
  const generativeModel = vertexAI.getGenerativeModel({
    model: model,
  });

  // Create a chat session and pass your function declarations
  const chat = generativeModel.startChat({
    tools: functionDeclarations,
  });

  const chatInput1 = 'What is the weather in Boston?';

  // This should include a functionCall response from the model
  const result1 = await chat.sendMessageStream(chatInput1);
  for await (const item of result1.stream) {
    console.log(item.candidates[0]);
  }
  await result1.response;

  // Send a follow up message with a FunctionResponse
  const result2 = await chat.sendMessageStream(functionResponseParts);
  for await (const item of result2.stream) {
    console.log(item.candidates[0]);
  }

  // This should include a text response from the model using the response content
  // provided above
  const response2 = await result2.response;
  console.log(response2.candidates[0].content.parts[0].text);
}

Parallel function calling example

For prompts such as "Get weather details in New Delhi and San Francisco?", the model may propose several parallel function calls. For a list of models that support parallel function calling, see Supported models.

REST

This example demonstrates a scenario with one get_current_weather function. The user prompt is "Get weather details in New Delhi and San Francisco?". The model proposes two parallel get_current_weather function calls: one with the parameter New Delhi and the other with the parameter San Francisco.

To learn more about the parameters of the model request, see Gemini API.

{
"candidates": [
  {
    "content": {
      "role": "model",
      "parts": [
        {
          "functionCall": {
            "name": "get_current_weather",
            "args": {
              "location": "New Delhi"
            }
          }
        },
        {
          "functionCall": {
            "name": "get_current_weather",
            "args": {
              "location": "San Francisco"
            }
          }
        }
      ]
    },
    ...
  }
],
...
}

The following command demonstrates how you can provide the function output to the model. Replace my-project with the name of your Google Cloud project.

Model request

PROJECT_ID=my-project
MODEL_ID=gemini-1.5-pro-002
VERSION="v1"
LOCATION="us-central1"
ENDPOINT=${LOCATION}-aiplatform.googleapis.com
API="generateContent"
curl -X POST -H "Authorization: Bearer $(gcloud auth print-access-token)" -H "Content-Type: application/json"  https://${ENDPOINT}/${VERSION}/projects/${PROJECT_ID}/locations/${LOCATION}/publishers/google/models/${MODEL_ID}:${API} -d '{
"contents": [
    {
        "role": "user",
        "parts": {
            "text": "What is difference in temperature in New Delhi and San Francisco?"
        }
    },
    {
        "role": "model",
        "parts": [
            {
                "functionCall": {
                    "name": "get_current_weather",
                    "args": {
                        "location": "New Delhi"
                    }
                }
            },
            {
                "functionCall": {
                    "name": "get_current_weather",
                    "args": {
                        "location": "San Francisco"
                    }
                }
            }
        ]
    },
    {
        "role": "user",
        "parts": [
            {
                "functionResponse": {
                    "name": "get_current_weather",
                    "response": {
                        "temperature": 30.5,
                        "unit": "C"
                    }
                }
            },
            {
                "functionResponse": {
                    "name": "get_current_weather",
                    "response": {
                        "temperature": 20,
                        "unit": "C"
                    }
                }
            }
        ]
    }
],
"tools": [
    {
        "function_declarations": [
            {
                "name": "get_current_weather",
                "description": "Get the current weather in a specific location",
                "parameters": {
                    "type": "object",
                    "properties": {
                        "location": {
                            "type": "string",
                            "description": "The city and state, e.g. San Francisco, CA or a zip code e.g. 95616"
                        }
                    },
                    "required": [
                        "location"
                    ]
                }
            }
        ]
    }
]
}'

The natural language response created by the model is similar to the following:

Model response

[
{
    "candidates": [
        {
            "content": {
                "parts": [
                    {
                        "text": "The temperature in New Delhi is 30.5C and the temperature in San Francisco is 20C. The difference is 10.5C. \n"
                    }
                ]
            },
            "finishReason": "STOP",
            ...
        }
    ]
    ...
}
]

Python 

import vertexai

from vertexai.generative_models import (
    FunctionDeclaration,
    GenerativeModel,
    Part,
    Tool,
)

# TODO(developer): Update & uncomment below line
# PROJECT_ID = "your-project-id"

# Initialize Vertex AI
vertexai.init(project=PROJECT_ID, location="us-central1")

# Specify a function declaration and parameters for an API request
function_name = "get_current_weather"
get_current_weather_func = FunctionDeclaration(
    name=function_name,
    description="Get the current weather in a given location",
    parameters={
        "type": "object",
        "properties": {
            "location": {
                "type": "string",
                "description": "The location for which to get the weather. \
                  It can be a city name, a city name and state, or a zip code. \
                  Examples: 'San Francisco', 'San Francisco, CA', '95616', etc.",
            },
        },
    },
)

# In this example, we'll use synthetic data to simulate a response payload from an external API
def mock_weather_api_service(location: str) -> str:
    temperature = 25 if location == "San Francisco" else 35
    return f"""{{ "location": "{location}", "temperature": {temperature}, "unit": "C" }}"""

# Define a tool that includes the above function
tools = Tool(
    function_declarations=[get_current_weather_func],
)

# Initialize Gemini model
model = GenerativeModel(
    model_name="gemini-1.5-pro-002",
    tools=[tools],
)

# Start a chat session
chat_session = model.start_chat()
response = chat_session.send_message(
    "Get weather details in New Delhi and San Francisco?"
)

function_calls = response.candidates[0].function_calls
print("Suggested finction calls:\n", function_calls)

if function_calls:
    api_responses = []
    for func in function_calls:
        if func.name == function_name:
            api_responses.append(
                {
                    "content": mock_weather_api_service(
                        location=func.args["location"]
                    )
                }
            )

    # Return the API response to Gemini
    response = chat_session.send_message(
        [
            Part.from_function_response(
                name="get_current_weather",
                response=api_responses[0],
            ),
            Part.from_function_response(
                name="get_current_weather",
                response=api_responses[1],
            ),
        ],
    )

    print(response.text)
    # Example response:
    # The current weather in New Delhi is 35°C. The current weather in San Francisco is 25°C.

Go 

import (
	"context"
	"encoding/json"
	"errors"
	"fmt"
	"io"

	"cloud.google.com/go/vertexai/genai"
)

// parallelFunctionCalling shows how to execute multiple function calls in parallel
// and return their results to the model for generating a complete response.
func parallelFunctionCalling(w io.Writer, projectID, location, modelName string) error {
	// location = "us-central1"
	// modelName = "gemini-1.5-flash-002"
	ctx := context.Background()
	client, err := genai.NewClient(ctx, projectID, location)
	if err != nil {
		return fmt.Errorf("failed to create GenAI client: %w", err)
	}
	defer client.Close()

	model := client.GenerativeModel(modelName)
	// Set temperature to 0.0 for maximum determinism in function calling.
	model.SetTemperature(0.0)

	funcName := "getCurrentWeather"
	funcDecl := &genai.FunctionDeclaration{
		Name:        funcName,
		Description: "Get the current weather in a given location",
		Parameters: &genai.Schema{
			Type: genai.TypeObject,
			Properties: map[string]*genai.Schema{
				"location": {
					Type: genai.TypeString,
					Description: "The location for which to get the weather. " +
						"It can be a city name, a city name and state, or a zip code. " +
						"Examples: 'San Francisco', 'San Francisco, CA', '95616', etc.",
				},
			},
			Required: []string{"location"},
		},
	}
	// Add the weather function to our model toolbox.
	model.Tools = []*genai.Tool{
		{
			FunctionDeclarations: []*genai.FunctionDeclaration{funcDecl},
		},
	}

	prompt := genai.Text("Get weather details in New Delhi and San Francisco?")
	resp, err := model.GenerateContent(ctx, prompt)

	if err != nil {
		return fmt.Errorf("failed to generate content: %w", err)
	}
	if len(resp.Candidates) == 0 {
		return errors.New("got empty response from model")
	} else if len(resp.Candidates[0].FunctionCalls()) == 0 {
		return errors.New("got no function call suggestions from model")
	}

	// In a production environment, consider adding validations for function names and arguments.
	for _, fnCall := range resp.Candidates[0].FunctionCalls() {
		fmt.Fprintf(w, "The model suggests to call the function %q with args: %v\n", fnCall.Name, fnCall.Args)
		// Example response:
		// The model suggests to call the function "getCurrentWeather" with args: map[location:New Delhi]
		// The model suggests to call the function "getCurrentWeather" with args: map[location:San Francisco]
	}

	// Use synthetic data to simulate responses from the external API.
	// In a real application, this would come from an actual weather API.
	mockAPIResp1, err := json.Marshal(map[string]string{
		"location":         "New Delhi",
		"temperature":      "42",
		"temperature_unit": "C",
		"description":      "Hot and humid",
		"humidity":         "65",
	})
	if err != nil {
		return fmt.Errorf("failed to marshal function response to JSON: %w", err)
	}

	mockAPIResp2, err := json.Marshal(map[string]string{
		"location":         "San Francisco",
		"temperature":      "36",
		"temperature_unit": "F",
		"description":      "Cold and cloudy",
		"humidity":         "N/A",
	})
	if err != nil {
		return fmt.Errorf("failed to marshal function response to JSON: %w", err)
	}

	// Note, that the function calls don't have to be chained. We can obtain both responses in parallel
	// and return them to Gemini at once.
	funcResp1 := &genai.FunctionResponse{
		Name: funcName,
		Response: map[string]any{
			"content": mockAPIResp1,
		},
	}
	funcResp2 := &genai.FunctionResponse{
		Name: funcName,
		Response: map[string]any{
			"content": mockAPIResp2,
		},
	}

	// Return both API responses to the model allowing it to complete its response.
	resp, err = model.GenerateContent(ctx, prompt, funcResp1, funcResp2)
	if err != nil {
		return fmt.Errorf("failed to generate content: %w", err)
	}
	if len(resp.Candidates) == 0 || len(resp.Candidates[0].Content.Parts) == 0 {
		return errors.New("got empty response from model")
	}

	fmt.Fprintln(w, resp.Candidates[0].Content.Parts[0])
	// Example response:
	// The weather in New Delhi is hot and humid with a humidity of 65 and a temperature of 42°C. The weather in San Francisco ...

	return nil
}

Best practices for function calling

Function name

Function name should start with a letter or an underscore and contains only characters a-z, A-Z, 0-9, underscores, dots or dashes with a maximum length of 64.

Function description

Write function descriptions clearly and verbosely. For example, for a book_flight_ticket function:

  • The following is an example of a good function description: book flight tickets after confirming users' specific requirements, such as time, departure, destination, party size and preferred airline
  • The following is an example of a bad function description: book flight ticket

Function parameters

Function parameter and nested attribute names should start with a letter or an underscore and contains only characters a-z, A-Z, 0-9, or underscores with a maximum length of 64. Don't use period (.), dash (-), or space characters in the function parameter names and nested attributes. Instead, use underscore (_) characters or any other characters.

Descriptions

Write clear and verbose parameter descriptions, including details such as your preferred format or values. For example, for a book_flight_ticket function:

  • The following is a good example of a departure parameter description: Use the 3 char airport code to represent the airport. For example, SJC or SFO. Don't use the city name.
  • The following is a bad example of a departure parameter description: the departure airport

Types

If possible, use strongly typed parameters to reduce model hallucinations. For example, if the parameter values are from a finite set, add an enum field instead of putting the set of values into the description. If the parameter value is always an integer, set the type to integer rather than number.

System instructions

When using functions with date, time, or location parameters, include the current date, time, or relevant location information (for example, city and country) in the system instruction. This ensures the model has the necessary context to process the request accurately, even if the user's prompt lacks details.

User prompt

For best results, prepend the user prompt with the following details:

  • Additional context for the model-for example, You are a flight API assistant to help with searching flights based on user preferences.
  • Details or instructions on how and when to use the functions-for example, Don't make assumptions on the departure or destination airports. Always use a future date for the departure or destination time.
  • Instructions to ask clarifying questions if user queries are ambiguous-for example, Ask clarifying questions if not enough information is available.

Generation configuration

For the temperature parameter, use 0 or another low value. This instructs the model to generate more confident results and reduces hallucinations.

API invocation

If the model proposes the invocation of a function that would send an order, update a database, or otherwise have significant consequences, validate the function call with the user before executing it.

Pricing

The pricing for function calling is based on the number of characters within the text inputs and outputs. To learn more, see Vertex AI pricing.

Here, text input (prompt) refers to the user prompt for the current conversation turn, the function declarations for the current conversation turn, and the history of the conversation. The history of the conversation includes the queries, the function calls, and the function responses of previous conversation turns. Vertex AI truncates the history of the conversation at 32,000 characters.

Text output (response) refers to the function calls and the text responses for the current conversation turn.

What's next