Controlled generation JSON output with predefined schema

This code sample demonstrates how to use the `response_mime_type` and `response_schema` parameters to get a response that follows the JSON format and schema that you've defined.

Explore further

For detailed documentation that includes this code sample, see the following:

• Controlled generation

Code sample

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.

public async Task<string> GenerateContentWithResponseSchema2(
    string projectId = "your-project-id",
    string location = "us-central1",
    string publisher = "google",
    string model = "gemini-1.5-pro-001")
{

    var predictionServiceClient = new PredictionServiceClientBuilder
    {
        Endpoint = $"{location}-aiplatform.googleapis.com"
    }.Build();

    var responseSchema = new OpenApiSchema
    {
        Type = Type.Array,
        Items = new()
        {
            Type = Type.Object,
            Properties =
            {
                ["rating"] = new() { Type = Type.Integer },
                ["flavor"] = new() { Type = Type.String }
            },
            Required = { "rating", "flavor" }
        }
    };

    string prompt = @"
        Reviews from our social media:

        - ""Absolutely loved it! Best ice cream I've ever had."" Rating: 4, Flavor: Strawberry Cheesecake
        - ""Quite good, but a bit too sweet for my taste."" Rating: 1, Flavor: Mango Tango";

    var generateContentRequest = new GenerateContentRequest
    {
        Model = $"projects/{projectId}/locations/{location}/publishers/{publisher}/models/{model}",
        Contents =
        {
            new Content
            {
                Role = "USER",
                Parts =
                {
                    new Part { Text = prompt }
                }
            }
        },
        GenerationConfig = new GenerationConfig
        {
            ResponseMimeType = "application/json",
            ResponseSchema = responseSchema
        },
    };

    GenerateContentResponse response = await predictionServiceClient.GenerateContentAsync(generateContentRequest);

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

    return responseText;
}

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"
	"errors"
	"fmt"
	"io"

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

// controlledGenerationResponseSchema2 shows how to make sure the generated output
// will always be valid JSON and adhere to a specific schema.
func controlledGenerationResponseSchema2(w io.Writer, projectID, location, modelName string) error {
	// location := "us-central1"
	// modelName := "gemini-1.5-pro-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)

	model.GenerationConfig.ResponseMIMEType = "application/json"

	// Build an OpenAPI schema, in memory
	model.GenerationConfig.ResponseSchema = &genai.Schema{
		Type: genai.TypeArray,
		Items: &genai.Schema{
			Type: genai.TypeArray,
			Items: &genai.Schema{
				Type: genai.TypeObject,
				Properties: map[string]*genai.Schema{
					"rating": {
						Type: genai.TypeInteger,
					},
					"flavor": {
						Type: genai.TypeString,
					},
				},
			},
		},
	}

	prompt := `
		Reviews from our social media:

		- "Absolutely loved it! Best ice cream I've ever had." Rating: 4, Flavor: Strawberry Cheesecake
		- "Quite good, but a bit too sweet for my taste." Rating: 1, Flavor: Mango Tango
	`

	res, err := model.GenerateContent(ctx, genai.Text(prompt))
	if err != nil {
		return fmt.Errorf("unable to generate contents: %v", err)
	}

	if len(res.Candidates) == 0 ||
		len(res.Candidates[0].Content.Parts) == 0 {
		return errors.New("empty response from model")
	}

	fmt.Fprint(w, res.Candidates[0].Content.Parts[0])
	return nil
}

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.GenerateContentResponse;
import com.google.cloud.vertexai.api.GenerationConfig;
import com.google.cloud.vertexai.api.Schema;
import com.google.cloud.vertexai.api.Type;
import com.google.cloud.vertexai.generativeai.GenerativeModel;
import com.google.cloud.vertexai.generativeai.ResponseHandler;
import java.io.IOException;
import java.util.Arrays;

public class ControlledGenerationSchema2 {
  public static void main(String[] args) throws IOException {
    // TODO(developer): Replace these variables before running the sample.
    String projectId = "genai-java-demos";
    String location = "us-central1";
    String modelName = "gemini-1.5-pro-001";

    controlGenerationWithJsonSchema2(projectId, location, modelName);
  }

  // Generate responses that are always valid JSON and comply with a JSON schema
  public static String controlGenerationWithJsonSchema2(
      String projectId, String location, String modelName)
      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)) {
      GenerationConfig generationConfig = GenerationConfig.newBuilder()
          .setResponseMimeType("application/json")
          .setResponseSchema(Schema.newBuilder()
              .setType(Type.ARRAY)
              .setItems(Schema.newBuilder()
                  .setType(Type.OBJECT)
                  .putProperties("rating", Schema.newBuilder().setType(Type.INTEGER).build())
                  .putProperties("flavor", Schema.newBuilder().setType(Type.STRING).build())
                  .addAllRequired(Arrays.asList("rating", "flavor"))
                  .build())
              .build())
          .build();

      GenerativeModel model = new GenerativeModel(modelName, vertexAI)
          .withGenerationConfig(generationConfig);

      GenerateContentResponse response = model.generateContent(
          "Reviews from our social media:\n"
              + "\"Absolutely loved it! Best ice cream I've ever had.\" "
              + "Rating: 4, Flavor: Strawberry Cheesecake\n"
              + "\"Quite good, but a bit too sweet for my taste.\" "
              + "Rating: 1, Flavor: Mango Tango"
      );

      String output = ResponseHandler.getText(response);
      System.out.println(output);
      return output;
    }
  }
}

Python

Before trying this sample, follow the Python setup instructions in the Vertex AI quickstart using client libraries. For more information, see the Vertex AI Python 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 vertexai

from vertexai.generative_models import GenerationConfig, GenerativeModel

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

response_schema = {
    "type": "ARRAY",
    "items": {
        "type": "ARRAY",
        "items": {
            "type": "OBJECT",
            "properties": {
                "rating": {"type": "INTEGER"},
                "flavor": {"type": "STRING"},
            },
        },
    },
}

prompt = """
    Reviews from our social media:
    - "Absolutely loved it! Best ice cream I've ever had." Rating: 4, Flavor: Strawberry Cheesecake
    - "Quite good, but a bit too sweet for my taste." Rating: 1, Flavor: Mango Tango
"""

model = GenerativeModel("gemini-1.5-pro-002")

response = model.generate_content(
    prompt,
    generation_config=GenerationConfig(
        response_mime_type="application/json", response_schema=response_schema
    ),
)

print(response.text)
# Example response:
# [
#     [
#         {"flavor": "Strawberry Cheesecake", "rating": 4},
#         {"flavor": "Mango Tango", "rating": 1},
#     ]
# ]

What's next

To search and filter code samples for other Google Cloud products, see the Google Cloud sample browser.