Function calling reference

Function calling improves the LLMs ability to provide relevant and contextual answers.

You can provide custom functions to a generative AI model with the Function Calling API. The model doesn't directly invoke these functions, but instead generates structured data output that specifies the function name and suggested arguments.

This output enables the calling of external APIs or information systems such as databases, customer relationship management systems, and document repositories. The resulting API output can be used by the LLM to improve response quality.

For more conceptual documentation on function calling, see Function calling.

Supported Models:

Model	Version
Gemini 1.5 Flash	gemini-1.5-flash-002 gemini-1.5-flash-001
Gemini 1.5 Pro	gemini-1.5-pro-002 gemini-1.5-pro-001
Gemini 1.0 Pro	gemini-1.0-pro-001 gemini-1.0-pro-002

Limitations:

• The maximum number of function declarations that can be provided with the request is 128.
• FunctionCallingConfig.Mode.ANY is available with only the Gemini 1.5 Pro and Gemini 1.5 Flash models.

Example syntax

Syntax to send a function call API request.

curl

curl -X POST \
  -H "Authorization: Bearer $(gcloud auth print-access-token)" \
  -H "Content-Type: application/json" \

https://${LOCATION}-aiplatform.googleapis.com/v1/projects/${PROJECT_ID}/locations/${LOCATION}/publishers/google/models/${MODEL_ID}:generateContent \
-d '{
  "contents": [{
    ...
  }],
  "tools": [{
    "function_declarations": [
      {
        ...
      }
    ]
  }]
}'

Python

gemini_model = GenerativeModel(
    MODEL_ID,
    generation_config=generation_config,
    tools=[
        Tool(
            function_declarations=[
                FunctionDeclaration(
                    ...
                )
            ]
        )
    ],
)

Parameter list

See examples for implementation details.

FunctionDeclaration

Defines a function that the model can generate JSON inputs for based on OpenAPI 3.0 specifications.

Parameters
name	string The name of the function to call. Must start with a letter or an underscore. Must be a-z, A-Z, 0-9, or contains underscores, dots, or dashes, with a maximum length of 64.
description	Optional: string The description and purpose of the function. The model uses this to decide how and whether to call the function. For the best results, we recommend that you include a description.
parameters	Optional: Schema Describes the parameters of the function in the OpenAPI JSON Schema Object format: OpenAPI 3.0 specification.
response	Optional: Schema Describes the output from the function in the OpenAPI JSON Schema Object format: OpenAPI 3.0 specification.

For more information, see Function calling

Schema

Defines the format of the input and output data in a function call based on the OpenAPI 3.0 Schema specification.

Parameters
type	string Enum. The type of the data. Must be one of: STRING INTEGER BOOLEAN NUMBER ARRAY OBJECT
description	Optional: string Description of the data.
enum	Optional: string[] Possible values of the element of primitive type with enum format.
items	Optional: Schema[] Schema of the elements of Type.ARRAY
properties	Optional: Schema Schema of the properties of Type.OBJECT
required	Optional: string[] Required properties of Type.OBJECT.
nullable	Optional: bool Indicates if the value may be null.

FunctionCallingConfig

The FunctionCallingConfig controls the behavior of the model and determines what type of function to call.

Parameters
mode	Optional: enum/string[] AUTO: Default model behavior. The model can make predictions in either a function call form or a natural language response form. The model decides which form to use based on the context. NONE: The model doesn't make any predictions in the form of function calls. 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.
allowed_function_names	Optional: string[] Function names to call. Only set when the mode is ANY. Function names should match [FunctionDeclaration.name]. With mode set to ANY, the model will predict a function call from the set of function names provided.

Examples

Send a function declaration

The following example is a basic example of sending a query and a function declaration to the model.

REST

Before using any of the request data, make the following replacements:

• PROJECT_ID: Your project ID.
• LOCATION: The region to process the request.
• MODEL_ID: The ID of the model that's being processed.
• ROLE: The identity of the entity that creates the message.
• TEXT: The prompt to send to the model.
• NAME: The name of the function to call.
• DESCRIPTION: Description and purpose of the function.
• For other fields, see the Parameter list table.

HTTP method and URL:

POST https://LOCATION-aiplatform.googleapis.com/v1/projects/PROJECT_ID/locations/LOCATION/publishers/google/models/MODEL_ID:generateContent

Request JSON body:

{
  "contents": [{
    "role": "ROLE",
    "parts": [{
      "text": "TEXT"
    }]
  }],
  "tools": [{
    "function_declarations": [
      {
        "name": "NAME",
        "description": "DESCRIPTION",
        "parameters": {
          "type": "TYPE",
          "properties": {
            "location": {
              "type": "TYPE",
              "description": "DESCRIPTION"
            }
          },
          "required": [
            "location"
          ]
        }
      }
    ]
  }]
}

To send your request, choose one of these options:

curl

Note: The following command assumes that you have logged in to the gcloud CLI with your user account by running gcloud init or gcloud auth login , or by using Cloud Shell, which automatically logs you into the gcloud CLI . You can check the currently active account by running gcloud auth list.

Save the request body in a file named request.json, and execute the following command:

curl -X POST \
     -H "Authorization: Bearer $(gcloud auth print-access-token)" \
     -H "Content-Type: application/json; charset=utf-8" \
     -d @request.json \
     "https://LOCATION-aiplatform.googleapis.com/v1/projects/PROJECT_ID/locations/LOCATION/publishers/google/models/MODEL_ID:generateContent"

PowerShell

Note: The following command assumes that you have logged in to the gcloud CLI with your user account by running gcloud init or gcloud auth login . You can check the currently active account by running gcloud auth list.

Save the request body in a file named request.json, and execute the following command:

$cred = gcloud auth print-access-token
$headers = @{ "Authorization" = "Bearer $cred" }

Invoke-WebRequest `
    -Method POST `
    -Headers $headers `
    -ContentType: "application/json; charset=utf-8" `
    -InFile request.json `
    -Uri "https://LOCATION-aiplatform.googleapis.com/v1/projects/PROJECT_ID/locations/LOCATION/publishers/google/models/MODEL_ID:generateContent" | Select-Object -Expand Content

Example curl command

PROJECT_ID=myproject
LOCATION=us-central1
MODEL_ID=gemini-1.0-pro-002

curl -X POST \
  -H "Authorization: Bearer $(gcloud auth print-access-token)" \
  -H "Content-Type: application/json" \
  https://${LOCATION}-aiplatform.googleapis.com/v1/projects/${PROJECT_ID}/locations/${LOCATION}/publishers/google/models/${MODEL_ID}:generateContent \
  -d '{
    "contents": [{
      "role": "user",
      "parts": [{
        "text": "What is the weather in Boston?"
      }]
    }],
    "tools": [{
      "functionDeclarations": [
        {
          "name": "get_current_weather",
          "description": "Get the current weather in a given 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"
            ]
          }
        }
      ]
    }]
  }'

Python

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

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'],
        },
      },
    ],
  },
];

/**
 * TODO(developer): Update these variables before running the sample.
 */
async function functionCallingBasic(
  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.preview.getGenerativeModel({
    model: model,
  });

  const request = {
    contents: [
      {role: 'user', parts: [{text: 'What is the weather in Boston?'}]},
    ],
    tools: functionDeclarations,
  };
  const result = await generativeModel.generateContent(request);
  console.log(JSON.stringify(result.response.candidates[0].content));
}

Java

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

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

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

// functionCallsBasic opens a chat session and sends 2 messages to the model:
// - first, to convert a text into a structured function call request
// - second, to convert a structured function call response into natural language.
// Writes output of second call to w.
func functionCallsBasic(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
	params := &genai.Schema{
		Type: genai.TypeObject,
		Properties: map[string]*genai.Schema{
			"location": {
				Type:        genai.TypeString,
				Description: "location",
			},
		},
	}
	fundecl := &genai.FunctionDeclaration{
		Name:        "getCurrentWeather",
		Description: "Get the current weather in a given location",
		Parameters:  params,
	}
	model.Tools = []*genai.Tool{
		{FunctionDeclarations: []*genai.FunctionDeclaration{fundecl}},
	}

	chat := model.StartChat()

	resp, err := chat.SendMessage(ctx, genai.Text("What's the weather like in Boston?"))
	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 `getCurrentWeather`
	// with a value for the argument `location`.
	_, err = json.MarshalIndent(resp.Candidates[0].Content.Parts[0], "", "  ")
	if err != nil {
		return fmt.Errorf("json.MarshalIndent: %w", err)
	}

	// In this example, we'll use synthetic data to simulate a response payload from an external API
	weather := map[string]string{
		"location":    "Boston",
		"temperature": "38",
		"description": "Partly Cloudy",
		"icon":        "partly-cloudy",
		"humidity":    "65",
		"wind":        "{\"speed\": \"10\", \"direction\": \"NW\"}",
	}
	weather_json, _ := json.Marshal(weather)

	// Create a function call response, to simulate the result of a call to a
	// real service
	funresp := &genai.FunctionResponse{
		Name: "getCurrentWeather",
		Response: map[string]any{
			"currentWeather": weather_json,
		},
	}
	_, err = json.MarshalIndent(funresp, "", "  ")
	if err != nil {
		return fmt.Errorf("json.MarshalIndent: %w", err)
	}

	// 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.
	content, err := json.MarshalIndent(resp.Candidates[0].Content.Parts[0], "", "  ")
	if err != nil {
		return fmt.Errorf("json.MarshalIndent: %w", err)
	}

	fmt.Fprintf(w, "generated summary:\n%s\n", content)
	return nil
}

REST (OpenAI)

You can call the Function Calling API by using the OpenAI library. For more information, see Call Vertex AI models by using the OpenAI library.

Before using any of the request data, make the following replacements:

• PROJECT_ID: Your project ID.
• LOCATION: The region to process the request.
• MODEL_ID: The ID of the model that's being processed.

HTTP method and URL:

POST https://LOCATION-aiplatform.googleapis.com/v1beta1/projects/PROJECT_ID/locations/LOCATION/endpoints/openapi/chat/completions

Request JSON body:

{
  "model": "google/MODEL_ID",
  "messages": [
    {
      "role": "user",
      "content": "What is the weather in Boston?"
    }
  ],
  "tools": [
    {
      "type": "function",
      "function": {
        "name": "get_current_weather",
        "description": "Get the current weather in a given 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"]
        }
      }
    }
  ]
}

To send your request, choose one of these options:

curl

Note: The following command assumes that you have logged in to the gcloud CLI with your user account by running gcloud init or gcloud auth login , or by using Cloud Shell, which automatically logs you into the gcloud CLI . You can check the currently active account by running gcloud auth list.

Save the request body in a file named request.json, and execute the following command:

curl -X POST \
     -H "Authorization: Bearer $(gcloud auth print-access-token)" \
     -H "Content-Type: application/json; charset=utf-8" \
     -d @request.json \
     "https://LOCATION-aiplatform.googleapis.com/v1beta1/projects/PROJECT_ID/locations/LOCATION/endpoints/openapi/chat/completions"

PowerShell

Note: The following command assumes that you have logged in to the gcloud CLI with your user account by running gcloud init or gcloud auth login . You can check the currently active account by running gcloud auth list.

Save the request body in a file named request.json, and execute the following command:

$cred = gcloud auth print-access-token
$headers = @{ "Authorization" = "Bearer $cred" }

Invoke-WebRequest `
    -Method POST `
    -Headers $headers `
    -ContentType: "application/json; charset=utf-8" `
    -InFile request.json `
    -Uri "https://LOCATION-aiplatform.googleapis.com/v1beta1/projects/PROJECT_ID/locations/LOCATION/endpoints/openapi/chat/completions" | Select-Object -Expand Content

Python (OpenAI)

You can call the Function Calling API by using the OpenAI library. For more information, see Call Vertex AI models by using the OpenAI library.

import vertexai
import openai

from google.auth import default, transport

# TODO(developer): Update & uncomment below line
# PROJECT_ID = "your-project-id"
location = "us-central1"

vertexai.init(project=PROJECT_ID, location=location)

# Programmatically get an access token
credentials, _ = default(scopes=["https://www.googleapis.com/auth/cloud-platform"])
auth_request = transport.requests.Request()
credentials.refresh(auth_request)

# # OpenAI Client
client = openai.OpenAI(
    base_url=f"https://{location}-aiplatform.googleapis.com/v1beta1/projects/{PROJECT_ID}/locations/{location}/endpoints/openapi",
    api_key=credentials.token,
)

tools = [
    {
        "type": "function",
        "function": {
            "name": "get_current_weather",
            "description": "Get the current weather in a given 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"],
            },
        },
    }
]

messages = []
messages.append(
    {
        "role": "system",
        "content": "Don't make assumptions about what values to plug into functions. Ask for clarification if a user request is ambiguous.",
    }
)
messages.append({"role": "user", "content": "What is the weather in Boston?"})

response = client.chat.completions.create(
    model="google/gemini-1.5-flash-001",
    messages=messages,
    tools=tools,
)

print("Function:", response.choices[0].message.tool_calls[0].id)
print("Arguments:", response.choices[0].message.tool_calls[0].function.arguments)
# Example response:
# Function: get_current_weather
# Arguments: {"location":"Boston"}

Send a function declaration with FunctionCallingConfig

The following example demonstrates how to pass a FunctionCallingConfig to the model.

The functionCallingConfig ensures that the model output is always a specific function call. To configure:

• Set the function calling mode to ANY.

• Specify the function names that you want to use in allowed_function_names. If allowed_function_names is empty, any of the provided functions can be returned.

REST

PROJECT_ID=myproject
LOCATION=us-central1
MODEL_ID=gemini-1.5-pro-001

curl -X POST \
  -H "Authorization: Bearer $(gcloud auth print-access-token)" \
  -H "Content-Type: application/json" \
  https://${LOCATION}-aiplatform.googleapis.com/v1beta1/projects/${PROJECT_ID}/locations/${LOCATION}/publishers/google/models/${MODEL_ID}:generateContent \
  -d '{
    "contents": [{
      "role": "user",
      "parts": [{
        "text": "Do you have the White Pixel 8 Pro 128GB in stock in the US?"
      }]
    }],
    "tools": [{
      "functionDeclarations": [
        {
          "name": "get_product_sku",
          "description": "Get the available inventory for a Google products, e.g: Pixel phones, Pixel Watches, Google Home etc",
          "parameters": {
            "type": "object",
            "properties": {
              "product_name": {"type": "string", "description": "Product name"}
            }
          }
        },
        {
          "name": "get_store_location",
          "description": "Get the location of the closest store",
          "parameters": {
            "type": "object",
            "properties": {
              "location": {"type": "string", "description": "Location"}
            },
          }
        }
      ]
    }],
    "toolConfig": {
        "functionCallingConfig": {
            "mode":"ANY",
            "allowedFunctionNames": ["get_product_sku"]
      }
    },
    "generationConfig": {
      "temperature": 0.95,
      "topP": 1.0,
      "maxOutputTokens": 8192
    }
  }'

Python

import vertexai

from vertexai.preview.generative_models import (
    FunctionDeclaration,
    GenerativeModel,
    Tool,
    ToolConfig,
)

# 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_func = FunctionDeclaration(
    name="get_product_sku",
    description="Get the available inventory for a Google products, e.g: Pixel phones, Pixel Watches, Google Home etc",
    # Function parameters are specified in 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,
    ],
)

# Define a tool config for the above functions
retail_tool_config = ToolConfig(
    function_calling_config=ToolConfig.FunctionCallingConfig(
        # ANY mode forces the model to predict a function call
        mode=ToolConfig.FunctionCallingConfig.Mode.ANY,
        # List of functions that can be returned when the mode is ANY.
        # If the list is empty, any declared function can be returned.
        allowed_function_names=["get_product_sku"],
    )
)

model = GenerativeModel(
    model_name="gemini-1.5-flash-002",
    tools=[retail_tool],
    tool_config=retail_tool_config,
)
response = model.generate_content(
    "Do you have the Pixel 8 Pro 128GB in stock?",
)

print(response.candidates[0].function_calls)
# Example response:
# [
# name: "get_product_sku"
# args {
#   fields { key: "product_name" value { string_value: "Pixel 8 Pro 128GB" }}
#   }
# ]

Node.js

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

const functionDeclarations = [
  {
    function_declarations: [
      {
        name: 'get_product_sku',
        description:
          'Get the available inventory for a Google products, e.g: Pixel phones, Pixel Watches, Google Home etc',
        parameters: {
          type: FunctionDeclarationSchemaType.OBJECT,
          properties: {
            productName: {type: FunctionDeclarationSchemaType.STRING},
          },
        },
      },
      {
        name: 'get_store_location',
        description: 'Get the location of the closest store',
        parameters: {
          type: FunctionDeclarationSchemaType.OBJECT,
          properties: {
            location: {type: FunctionDeclarationSchemaType.STRING},
          },
        },
      },
    ],
  },
];

const toolConfig = {
  function_calling_config: {
    mode: 'ANY',
    allowed_function_names: ['get_product_sku'],
  },
};

const generationConfig = {
  temperature: 0.95,
  topP: 1.0,
  maxOutputTokens: 8192,
};

/**
 * TODO(developer): Update these variables before running the sample.
 */
async function functionCallingAdvanced(
  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.preview.getGenerativeModel({
    model: model,
  });

  const request = {
    contents: [
      {
        role: 'user',
        parts: [
          {text: 'Do you have the White Pixel 8 Pro 128GB in stock in the US?'},
        ],
      },
    ],
    tools: functionDeclarations,
    tool_config: toolConfig,
    generation_config: generationConfig,
  };
  const result = await generativeModel.generateContent(request);
  console.log(JSON.stringify(result.response.candidates[0].content));
}

Go

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
}

REST (OpenAI)

You can call the Function Calling API by using the OpenAI library. For more information, see Call Vertex AI models by using the OpenAI library.

Before using any of the request data, make the following replacements:

• PROJECT_ID: Your project ID.
• LOCATION: The region to process the request.
• MODEL_ID: The ID of the model that's being processed.

HTTP method and URL:

POST https://LOCATION-aiplatform.googleapis.com/v1beta1/projects/PROJECT_ID/locations/LOCATION/endpoints/openapi/chat/completions

Request JSON body:

{
  "model": "google/MODEL_ID",
  "messages": [
  {
    "role": "user",
    "content": "What is the weather in Boston?"
  }
],
"tools": [
  {
    "type": "function",
    "function": {
      "name": "get_current_weather",
      "description": "Get the current weather in a given 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"]
      }
    }
  }
],
"tool_choice": "auto"
}

To send your request, choose one of these options:

curl

Note: The following command assumes that you have logged in to the gcloud CLI with your user account by running gcloud init or gcloud auth login , or by using Cloud Shell, which automatically logs you into the gcloud CLI . You can check the currently active account by running gcloud auth list.

Save the request body in a file named request.json, and execute the following command:

curl -X POST \
     -H "Authorization: Bearer $(gcloud auth print-access-token)" \
     -H "Content-Type: application/json; charset=utf-8" \
     -d @request.json \
     "https://LOCATION-aiplatform.googleapis.com/v1beta1/projects/PROJECT_ID/locations/LOCATION/endpoints/openapi/chat/completions"

PowerShell

Note: The following command assumes that you have logged in to the gcloud CLI with your user account by running gcloud init or gcloud auth login . You can check the currently active account by running gcloud auth list.

Save the request body in a file named request.json, and execute the following command:

$cred = gcloud auth print-access-token
$headers = @{ "Authorization" = "Bearer $cred" }

Invoke-WebRequest `
    -Method POST `
    -Headers $headers `
    -ContentType: "application/json; charset=utf-8" `
    -InFile request.json `
    -Uri "https://LOCATION-aiplatform.googleapis.com/v1beta1/projects/PROJECT_ID/locations/LOCATION/endpoints/openapi/chat/completions" | Select-Object -Expand Content

Python (OpenAI)

You can call the Function Calling API by using the OpenAI library. For more information, see Call Vertex AI models by using the OpenAI library.

import vertexai
import openai

from google.auth import default, transport

# TODO(developer): Update & uncomment below line
# PROJECT_ID = "your-project-id"
location = "us-central1"

vertexai.init(project=PROJECT_ID, location=location)

# Programmatically get an access token
credentials, _ = default(scopes=["https://www.googleapis.com/auth/cloud-platform"])
auth_request = transport.requests.Request()
credentials.refresh(auth_request)

# OpenAI Client
client = openai.OpenAI(
    base_url=f"https://{location}-aiplatform.googleapis.com/v1beta1/projects/{PROJECT_ID}/locations/{location}/endpoints/openapi",
    api_key=credentials.token,
)

tools = [
    {
        "type": "function",
        "function": {
            "name": "get_current_weather",
            "description": "Get the current weather in a given 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"],
            },
        },
    }
]

messages = []
messages.append(
    {
        "role": "system",
        "content": "Don't make assumptions about what values to plug into functions. Ask for clarification if a user request is ambiguous.",
    }
)
messages.append({"role": "user", "content": "What is the weather in Boston, MA?"})

response = client.chat.completions.create(
    model="google/gemini-1.5-flash-002",
    messages=messages,
    tools=tools,
    tool_choice="auto",
)

print("Function:", response.choices[0].message.tool_calls[0].id)
print("Arguments:", response.choices[0].message.tool_calls[0].function.arguments)
# Example response:
# Function: get_current_weather
# Arguments: {"location":"Boston"}

What's next

For detailed documentation, see the following:

• Function calling