ValidKit MCP server has clear, well-structured tool definitions with proper schemas and descriptions. All three tools are registered with Zod schemas, descriptions, and input validation. However, output schemas are not documented (tools return raw JSON.stringify of API responses), and error handling, while present, lacks actionable recovery guidance. Parameter descriptions are adequate but minimal. No tool annotations (readOnlyHint, idempotentHint) despite all tools being read-only. Tool names follow verb_noun convention (validate_*, check_*) and are unambiguous. The server demonstrates solid fundamentals but lacks polish in output documentation and error messaging.

• Document output schemas for each tool. Specify the structure of validate_email response (e.g., {deliverability: string, syntax_valid: boolean, mx_records: boolean, ...}), validate_emails_bulk summary (e.g., {valid_count: number, invalid_count: number, results: [...]}), and check_usage stats (e.g., {total_requests: number, valid_count: number, ...}).
• Enhance error messages with recovery guidance. Replace 'Rate limited: ... Wait a moment and try again.' with 'Rate limited (429). Wait 60 seconds before retrying. If this persists, upgrade your plan at https://validkit.com/pricing'.
• Add readOnlyHint: true to all three tool registrations. This signals to clients that these tools are safe to cache and parallelize.
• Expand parameter descriptions. For 'email', add format hint: 'Email address to validate (RFC 5322 format, e.g., [email protected])'. For 'emails', clarify: 'Array of email addresses (1-1000 items). Bulk validation is more efficient than sequential single validations.'
• Document the structure of bulk validation results. Clarify whether all 1000 results are returned in one response or paginated, and what fields each result contains (status, checks, suggestions, etc.).