gmail-mcp has well-structured tool definitions with consistent naming (verb_noun pattern), clear descriptions (avg ~120 chars), and complete input schemas. All 17 tools are explicitly registered with type-safe schemas. However, output schemas are not documented, error handling lacks recovery guidance, and several tools lack parameter constraints (enums, ranges). No tool annotations (readOnlyHint/destructiveHint) despite clear risk stratification. Parameter descriptions are adequate but could specify formats/constraints more explicitly. Missing idempotency guidance for write operations.

• Document output schemas for all tools. Specify field names, types, and structure. Example: 'Returns {messages: [{id, from, subject, snippet, timestamp}], total_count, next_cursor}'.
• Add tool annotations to the MCP server registration. Mark gmail_batch_trash, gmail_send, gmail_reply, gmail_forward, gmail_create_draft as destructiveHint=true or idempotentHint=true as appropriate.
• Add enum constraints to parameters with known valid values. Example: gmail_mark_read.read should be boolean (already correct); gmail_create_filter.archive should document boolean default=false.
• Document pagination for list tools. Specify: 'Returns up to 50 results by default. Use limit (1-50) and offset/cursor for pagination. Returns total_count for planning.'
• Add error recovery guidance in descriptions. Example: 'If message not found, verify the message ID with gmail_search() first.' This guides LLM retry logic.