generateImage

Tool call template

Replace each placeholder with a value matching the input schema. Only required parameters are included; add optional parameters as needed.

{
  "id": 1,
  "jsonrpc": "2.0",
  "method": "tools/call",
  "params": {
    "arguments": {
      "prompt": "<prompt>"
    },
    "name": "generateImage"
  }
}

Implementation Reference

• server.js:23-91 (registration)

  Full registration of the 'generateImage' MCP tool using server.tool(), including input schema, handler function, and tool metadata with parameter descriptions.

  server.tool(
    "generateImage",
    {
      prompt: z.string(),
      aspectRatio: z.string().optional(),
      outputFormat: z.string().optional()
    },
    async (params) => {
      // Default values
      const prompt = params.prompt || "Default image prompt";
      const aspectRatio = params.aspectRatio || "1:1";
      const outputFormat = params.outputFormat || "png";
  
      try {
        // Initialize the Imagen 3 model
        const model = genAI.getGenerativeModel({
          model: "gemini-2.0-flash-exp-image-generation",
          generationConfig: {
              responseModalities: ['Text', 'Image'],
          },
        });
  
        // Generate the image
        const result = await model.generateContent(prompt);
  
        // Extract the generated image data (base64 encoded)
        for (const part of result.response.candidates[0].content.parts) {
          // Based on the part type, either show the text or save the image
          if (part.text) {
            console.log(part.text);
            return {
              content: [{
                  type: "text",
                  text: part.text
              }]
            }
          } else if (part.inlineData) {
            const imageData = part.inlineData.data;
            const buffer = Buffer.from(imageData, 'base64');
            fs.writeFileSync('gemini-native-image.png', buffer);
            console.log('Image saved as gemini-native-image.png');
            return {
              content: [{
                type: "image",
                data: imageData,
                mimeType: `image/${outputFormat}`
              }]
            };
          }
        }
      } catch (error) {
        console.error("Image generation error:", error);
        return {
          content: [{
            type: "text",
            text: `Error generating image: ${error.message}`
          }]
        };
      }
    },
    {
      description: "Generate an image using Gemini API",
      parameters: {
        prompt: { type: "string", description: "The text description of the image to generate" },
        aspectRatio: { type: "string", description: "Aspect ratio of the image (e.g., '1:1', '16:9')", optional: true },
        outputFormat: { type: "string", description: "Output image format ('png' or 'jpeg')", optional: true }
      }
    }
  );

• server.js:30-82 (handler)

  The handler function for 'generateImage' tool. Uses GoogleGenerativeAI (Gemini model) to generate image from prompt, handles text or image parts in response, saves image to file, and returns MCP-formatted content (text or image).

  async (params) => {
    // Default values
    const prompt = params.prompt || "Default image prompt";
    const aspectRatio = params.aspectRatio || "1:1";
    const outputFormat = params.outputFormat || "png";
  
    try {
      // Initialize the Imagen 3 model
      const model = genAI.getGenerativeModel({
        model: "gemini-2.0-flash-exp-image-generation",
        generationConfig: {
            responseModalities: ['Text', 'Image'],
        },
      });
  
      // Generate the image
      const result = await model.generateContent(prompt);
  
      // Extract the generated image data (base64 encoded)
      for (const part of result.response.candidates[0].content.parts) {
        // Based on the part type, either show the text or save the image
        if (part.text) {
          console.log(part.text);
          return {
            content: [{
                type: "text",
                text: part.text
            }]
          }
        } else if (part.inlineData) {
          const imageData = part.inlineData.data;
          const buffer = Buffer.from(imageData, 'base64');
          fs.writeFileSync('gemini-native-image.png', buffer);
          console.log('Image saved as gemini-native-image.png');
          return {
            content: [{
              type: "image",
              data: imageData,
              mimeType: `image/${outputFormat}`
            }]
          };
        }
      }
    } catch (error) {
      console.error("Image generation error:", error);
      return {
        content: [{
          type: "text",
          text: `Error generating image: ${error.message}`
        }]
      };
    }
  },

• server.js:25-29 (schema)

  Zod schema for input validation of 'generateImage' tool parameters.

  {
    prompt: z.string(),
    aspectRatio: z.string().optional(),
    outputFormat: z.string().optional()
  },

• server.js:84-89 (schema)

  Tool metadata including description and JSON schema-like parameter definitions for 'generateImage'.

  description: "Generate an image using Gemini API",
  parameters: {
    prompt: { type: "string", description: "The text description of the image to generate" },
    aspectRatio: { type: "string", description: "Aspect ratio of the image (e.g., '1:1', '16:9')", optional: true },
    outputFormat: { type: "string", description: "Output image format ('png' or 'jpeg')", optional: true }
  }