Count tokens in a prompt

This sample demonstrates how to count the number of tokens in a prompt using the Vertex AI Gemini API.

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

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.


using Google.Cloud.AIPlatform.V1;
using System;
using System.Threading.Tasks;

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

        var request = new CountTokensRequest
        {
            Endpoint = $"projects/{projectId}/locations/{location}/publishers/{publisher}/models/{model}",
            Model = $"projects/{projectId}/locations/{location}/publishers/{publisher}/models/{model}",
            Contents =
            {
                new Content
                {
                    Role = "USER",
                    Parts = { new Part { Text = "Why is the sky blue?" } }
                }
            }
        };

        var response = await client.CountTokensAsync(request);
        int tokenCount = response.TotalTokens;
        Console.WriteLine($"There are {tokenCount} tokens in the prompt.");
        return tokenCount;
    }
}

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"
	"fmt"
	"io"

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

// countTokens returns the number of tokens for this prompt.
func countTokens(w io.Writer, prompt, projectID, location, modelName string) error {
	// prompt := "why is the sky blue?"
	// 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: %v", err)
	}
	defer client.Close()

	model := client.GenerativeModel(modelName)

	resp, err := model.CountTokens(ctx, genai.Text(prompt))
	if err != nil {
		return err
	}

	fmt.Fprintf(w, "Number of tokens for the prompt: %d\n", resp.TotalTokens)

	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.CountTokensResponse;
import com.google.cloud.vertexai.api.GenerateContentResponse;
import com.google.cloud.vertexai.generativeai.GenerativeModel;
import java.io.IOException;

public class GetTokenCount {
  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";

    getTokenCount(projectId, location, modelName);
  }

  // Gets the number of tokens for the prompt and the model's response.
  public static int getTokenCount(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)) {
      GenerativeModel model = new GenerativeModel(modelName, vertexAI);

      String textPrompt = "Why is the sky blue?";
      CountTokensResponse response = model.countTokens(textPrompt);

      int promptTokenCount = response.getTotalTokens();
      int promptCharCount = response.getTotalBillableCharacters();

      System.out.println("Prompt token Count: " + promptTokenCount);
      System.out.println("Prompt billable character count: " + promptCharCount);

      GenerateContentResponse contentResponse = model.generateContent(textPrompt);

      int tokenCount = contentResponse.getUsageMetadata().getPromptTokenCount();
      int candidateTokenCount = contentResponse.getUsageMetadata().getCandidatesTokenCount();
      int totalTokenCount = contentResponse.getUsageMetadata().getTotalTokenCount();

      System.out.println("Prompt token Count: " + tokenCount);
      System.out.println("Candidate Token Count: " + candidateTokenCount);
      System.out.println("Total token Count: " + totalTokenCount);

      return promptTokenCount;
    }
  }
}

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} = require('@google-cloud/vertexai');

/**
 * TODO(developer): Update these variables before running the sample.
 */
async function countTokens(
  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 req = {
    contents: [{role: 'user', parts: [{text: 'How are you doing today?'}]}],
  };

  const countTokensResp = await generativeModel.countTokens(req);
  console.log('count tokens response: ', countTokensResp);
}

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 GenerativeModel

# TODO(developer): Update and un-comment below line
# project_id = "PROJECT_ID"

vertexai.init(project=project_id, location="us-central1")

model = GenerativeModel(model_name="gemini-1.5-flash-001")

prompt = "Why is the sky blue?"

# Prompt tokens count
response = model.count_tokens(prompt)
print(f"Prompt Token Count: {response.total_tokens}")
print(f"Prompt Character Count: {response.total_billable_characters}")

# Send text to Gemini
response = model.generate_content(prompt)

# Response tokens count
usage_metadata = response.usage_metadata
print(f"Prompt Token Count: {usage_metadata.prompt_token_count}")
print(f"Candidates Token Count: {usage_metadata.candidates_token_count}")
print(f"Total Token Count: {usage_metadata.total_token_count}")

What's next

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