thumbnail

Instructions

Implementation Reference

• src/tools/index.ts:250-275 (handler)

  Executes the thumbnail extraction logic: loads image buffer, extracts thumbnail using exifr, converts to base64 data URL or base64, handles errors with standardized responses.

  async (args, extra) => {
    try {
      const { image, url } = args;
      const buf = await loadImage(image);
      const thumbnail = await exifr.thumbnail(buf);
      
      if (!thumbnail) {
        return createErrorResponse('No thumbnail found in image');
      }
      
      // Convert to base64 data URL by default
      if (!url) {
        const base64 = Buffer.from(thumbnail).toString('base64');
        const mimeType = 'image/jpeg'; // Thumbnails are typically JPEG
        const dataUrl = `data:${mimeType};base64,${base64}`;
        return createSuccessResponse({ dataUrl });
      }
      
      // For browsers, object URLs would be created, but we can't do that in Node
      // So we'll just return the base64 data
      const base64 = Buffer.from(thumbnail).toString('base64');
      return createSuccessResponse({ base64 });
    } catch (error) {
      return createErrorResponse(`Error extracting thumbnail: ${error instanceof Error ? error.message : String(error)}`);
    }
  }

• src/tools/index.ts:243-277 (registration)

  Registers the 'thumbnail' tool with the MCP server instance, defining its description, input schema, and handler function. Stores reference in tools object.

  // Tool 11: thumbnail - extracts embedded thumbnail
  const thumbnailTool = server.tool('thumbnail',
    "Extract embedded thumbnail from image as base64 data or URL",
    {
      image: ImageSourceSchema,
      url: z.boolean().optional()
    },
    async (args, extra) => {
      try {
        const { image, url } = args;
        const buf = await loadImage(image);
        const thumbnail = await exifr.thumbnail(buf);
        
        if (!thumbnail) {
          return createErrorResponse('No thumbnail found in image');
        }
        
        // Convert to base64 data URL by default
        if (!url) {
          const base64 = Buffer.from(thumbnail).toString('base64');
          const mimeType = 'image/jpeg'; // Thumbnails are typically JPEG
          const dataUrl = `data:${mimeType};base64,${base64}`;
          return createSuccessResponse({ dataUrl });
        }
        
        // For browsers, object URLs would be created, but we can't do that in Node
        // So we'll just return the base64 data
        const base64 = Buffer.from(thumbnail).toString('base64');
        return createSuccessResponse({ base64 });
      } catch (error) {
        return createErrorResponse(`Error extracting thumbnail: ${error instanceof Error ? error.message : String(error)}`);
      }
    }
  );
  tools['thumbnail'] = thumbnailTool;

• src/tools/index.ts:54-60 (schema)

  Zod schema for ImageSource used in thumbnail (and other) tool input parameters.

  const ImageSourceSchema = z.object({
    kind: z.enum(['path', 'url', 'base64', 'buffer']),
    path: z.string().optional(),
    url: z.string().optional(),
    data: z.string().optional(),
    buffer: z.string().optional()
  });

• src/types/image.ts:56-65 (schema)

  Dedicated Zod schema for thumbnail tool input (matches inline schema, though unused).

  export const ThumbnailSchema = z.object({
    image: z.object({
      kind: z.enum(['path', 'url', 'base64', 'buffer']),
      path: z.string().optional(),
      url: z.string().optional(),
      data: z.string().optional(),
      buffer: z.string().optional()
    }),
    url: z.boolean().optional()
  });