This Gmail MCP server demonstrates solid foundational quality with 20 well-structured tools covering email, label, and filter management. All tools have explicit descriptions (10-170 chars, well within the 10-1024 guideline) and complete JSON Schema definitions with proper type constraints and parameter descriptions. Zod schemas are properly compiled to JSON Schema. However, several patterns remain unimplemented: tool annotations (destructiveHint/readOnlyHint/idempotentHint) are absent, error handling lacks actionable recovery guidance, output schemas are not formally documented, and security gaps exist around rate limiting and audit logging. The naming convention is consistent and action-oriented (send_, delete_, create_, etc.), and parameter naming uses appropriate suffixes (_id, _email for disambiguation). Batch operations and template-based creation show good composition thinking. Most parameter descriptions adequately explain format and constraints, though some could be more explicit about ranges and dependencies.

• Add tool annotations to every tool registration. Mark read_email, search_emails, list_email_labels, list_filters, get_filter with readOnlyHint: true. Mark delete_email, batch_delete_emails, delete_label, delete_filter with destructiveHint: true. Mark send_email, draft_email, create_label, create_filter with appropriate hints based on idempotency.
• Document output schemas for all 20 tools. Create a response object for each, specifying returned fields, types, and whether they're required. Example: send_email returns { messageId: string; threadId?: string; timestamp: string }. This enables agents to chain results.
• Enhance error handling with actionable guidance. Instead of generic 'Error: Invalid recipient', return 'Invalid recipient email. Use search_emails(query: "to:@example.com") to find valid addresses in your account, or verify the email format is correct.'
• Add dry_run flag to destructive operations (delete_email, batch_delete_emails, delete_label, delete_filter). Dry-run returns what would be deleted without executing. This prevents accidental mass-deletion.
• Document rate limits and timeout expectations in tool descriptions. Example: 'batch_modify_emails processes up to 100 messages per request with a 30-second timeout. Requests exceeding 100 messages are rejected with a 429 error; retry with smaller batches after 60 seconds.'
• Verify OAuth token handling uses server-side injection (environment variables or vault) and is not exposed as a tool parameter. Add an explicit note in the README about credential security.