FRED MCP has well-structured tool definitions with complete input schemas and descriptions for all 5 tools. All tools follow verb_noun naming (fred_get_*, fred_search, fred_series_info, fred_category, fred_releases). Descriptions are substantive (100-200 chars), explaining WHAT each tool does and WHEN to use it. Parameters have types and descriptions. However, output schemas are NOT documented, the code shows fredFetch() returns raw API responses without specifying the structure LLMs should expect. Error handling is minimal (generic 'FRED API error' with status code). No enum constraints on optional parameters like 'frequency', 'units', 'order_by', 'sort_order', these accept free-form strings, inviting hallucinated values. The _apiKey parameter is exposed as a tool parameter (security anti-pattern), though the code does extract and delete it before use. Missing: output schema documentation, enum constraints, error recovery guidance, and per-tool permission declarations.

• Document output schemas for all tools. E.g., fred_get_series returns {series_id, count, observation_start, observation_end, observations: [{date, value}]}. Include field types and whether fields are always present.
• Move _apiKey from tool parameters to server-side environment variable injection. Update tool definitions to remove _apiKey from inputSchema. Extract key from process.env.FRED_API_KEY in callTool().
• Convert 'frequency', 'units', 'order_by', 'sort_order' to enum constraints in inputSchema. E.g., frequency: {type: 'string', enum: ['d', 'w', 'bw', 'm', 'q', 'sa', 'a']}. Remove free-text descriptions.
• Enhance error handling with recovery guidance. Catch specific FRED API errors (404 series not found, 400 invalid params) and return actionable messages: 'Series "INVALID" not found. Call fred_search(search_text="mortgage") to find valid series IDs.'
• Add pagination metadata to fred_search and fred_releases responses. Return {results: [...], total_count: N, limit: 20, offset: 0} so LLMs know when to paginate and can plan multi-call sequences.