Single tool with strong fundamentals: clear verb-noun naming (generate_image), detailed description (164 chars), complete input schema with all parameters typed and described, proper enum constraint for aspect_ratio, and good error handling with actionable messages. Output structure is well-formed with both text and image returns. However, some minor gaps prevent a higher score: output schema is not formally documented in code comments, parameter descriptions include example file paths (which LLMs may reuse literally), and no idempotent/destructive annotations despite write risk. The tool correctly handles secrets via environment variables (GEMINI_API_KEY, VERTEX_PROJECT).

• Add a TypeScript type export for the tool's return shape (e.g., `type GenerateImageResponse = { content: Array<{ type: 'text' | 'image'; text?: string; data?: string; mimeType?: string }> }`) and reference it in JSDoc so LLMs understand what fields to expect.
• Replace file path examples in descriptions with format constraints: instead of 'Example: C:/Users/palan/Pictures/output.png', write 'Any valid file path ending in .png (e.g., relative or absolute)'. Remove literal example values.
• Add toolAnnotations to the tool registration: set destructiveHint: true and idempotentHint: false to signal that repeated calls overwrite the output file. Register these in the server.registerTool() call.
• Document required permissions in the tool description: 'Requires GEMINI_API_KEY (AI Studio) or Vertex AI project credentials with image generation capability.' This clarifies setup requirements.
• Add retry guidance in error messages: if the API returns a rate limit or timeout error, include 'Retry this request after a short delay.' to guide agent recovery.
• Consider adding a model parameter validation: if the user passes an invalid model name, return 'Invalid model: got "<name>". Valid models include: gemini-3-pro-image-preview, gemini-2.5-flash-image'. This prevents silent failures.
• Document the image MIME type constraint in the tool description: 'Output format is always PNG or the format returned by the Gemini API (typically image/png or image/jpeg).' This clarifies what to expect.