Gemini MCP Server

Instructions

Implementation Reference

• src/tools/edit-image.ts:8-64 (handler)

  Main implementation of the edit_image tool. Contains the register function with tool metadata, input schema definition (lines 14-21), and the async handler function (lines 28-63) that processes image editing requests using Google's GenAI API.

  export function register(server: McpServer, ai: GoogleGenAI): void {
    server.registerTool(
      'edit_image',
      {
        title: 'Edit Image',
        description: 'Edit an image using a text prompt. Send a base64-encoded image and describe the desired changes.',
        inputSchema: {
          prompt: z.string().min(1).describe('Description of the edits to apply'),
          image: z.string().min(1).describe('Base64-encoded source image'),
          mimeType: z.enum(['image/png', 'image/jpeg', 'image/webp']).default('image/png').describe('MIME type of the source image'),
          model: ImageModel.default('gemini-3-pro-image-preview').describe('Image model to use (Nano Banana Pro by default)'),
          aspectRatio: AspectRatio.default('1:1').describe('Aspect ratio of the output image'),
          imageSize: ImageSize.default('1K').describe('Output image resolution'),
        },
        annotations: {
          readOnlyHint: true,
          destructiveHint: false,
          openWorldHint: true,
        },
      },
      async ({ prompt, image, mimeType, model, aspectRatio, imageSize }) => {
        try {
          const response = await ai.models.generateContent({
            model,
            contents: [
              { text: prompt },
              { inlineData: { mimeType, data: image } },
            ],
            config: {
              responseModalities: ['TEXT', 'IMAGE'],
              imageConfig: { aspectRatio, imageSize },
            },
          });
  
          const result = extractImageFromResponse(response);
          if (!result) {
            return {
              content: [{ type: 'text' as const, text: 'No edited image was produced. Try a different prompt.' }],
              isError: true,
            };
          }
  
          if (!validateImageSize(result.data)) {
            return {
              content: [{ type: 'text' as const, text: 'Edited image exceeds size limit. Try a smaller imageSize.' }],
              isError: true,
            };
          }
  
          return {
            content: [{ type: 'image' as const, data: result.data, mimeType: result.mimeType }],
          };
        } catch (error) {
          return formatToolError(error);
        }
      },
    );

• src/tools/edit-image.ts:14-21 (schema)

  Input schema definition for edit_image tool. Defines prompt, image, mimeType, model, aspectRatio, and imageSize parameters with Zod validation.

  inputSchema: {
    prompt: z.string().min(1).describe('Description of the edits to apply'),
    image: z.string().min(1).describe('Base64-encoded source image'),
    mimeType: z.enum(['image/png', 'image/jpeg', 'image/webp']).default('image/png').describe('MIME type of the source image'),
    model: ImageModel.default('gemini-3-pro-image-preview').describe('Image model to use (Nano Banana Pro by default)'),
    aspectRatio: AspectRatio.default('1:1').describe('Aspect ratio of the output image'),
    imageSize: ImageSize.default('1K').describe('Output image resolution'),
  },

• src/index.ts:9-9 (registration)

  Import statement for the edit_image tool registration functions.

  import { register as registerEditImage, registerMulti as registerEditImageMulti } from './tools/edit-image.js';

• src/index.ts:30-31 (registration)

  Registration of both edit_image and edit_image_multi tools with the MCP server.

  registerEditImage(server, ai);
  registerEditImageMulti(server, ai);

• src/utils/image.ts:8-20 (helper)

  Helper function extractImageFromResponse that extracts the base64 image data and MIME type from the GenAI API response.

  export function extractImageFromResponse(response: any): { data: string; mimeType: string } | null {
    const parts = response?.candidates?.[0]?.content?.parts;
    if (!parts) return null;
    for (const part of parts) {
      if (part.inlineData) {
        return {
          data: part.inlineData.data,
          mimeType: part.inlineData.mimeType,
        };
      }
    }
    return null;
  }