Single tool 'send_email' has a properly structured JSON Schema with all required parameters typed and described. However, the tool description is minimal (24 chars: 'Send an email via Gmail'), falling below the 50-200 char LLM-optimized baseline. Parameter descriptions are present but generic ('Email address to send to', 'Subject of the email', 'Body content of the email'). No output schema is documented, callers cannot predict the response structure. Error handling returns unstructured text ('success' boolean + 'messageId' or 'error' field) without recovery guidance. No mention of prerequisites (credentials, OAuth token), rate limits, or idempotency. The tool modifies state (sends email) but the description does not explicitly warn of irreversibility.

• Expand tool description to 80 - 150 chars: 'Send an email via Gmail. Requires valid OAuth2 credentials and token.json. Operation is irreversible, email is sent immediately. Returns messageId on success or error details on failure.'
• Document the output schema in the tool description or as a separate field: 'Returns {success: boolean, messageId?: string, message?: string, error?: string}'
• Add parameter descriptions that include constraints and examples: 'to: Valid email address (e.g. [email protected]). Required.' 'subject: Email subject line (1 - 200 chars). Required.' 'body: Email body in plain text or HTML (1 - 10000 chars). Required.'
• Enhance error messages with recovery guidance: Instead of 'Credentials file not found at /path', return 'Credentials file not found. Ensure CREDENTIALS_PATH env var points to a valid credentials.json file from Google Cloud Console.'
• Add a dry-run or confirmation pattern for this destructive operation. Consider a 'preview_email' tool that returns the formatted message without sending, allowing the agent to verify before calling send_email.

Inferred effective spec: <=2025-11-25.

• Relies on Logging (deprecated) - log to stderr or use OpenTelemetry