FRED MCP Server provides 2 tools with clear verb-based naming (search, series) and complete input schemas with proper type definitions and descriptions. Descriptions are adequate (145-180 chars, within the 10-1024 baseline range). Parameter descriptions are present and mostly detailed. However, output schemas are entirely undocumented, callers cannot see what fields to expect from responses. Error handling is minimal (generic HTTP errors with no recovery guidance or retry classification). Parameter relationships and constraints are inconsistently documented. No input validation, pagination metadata, or result limits are mentioned. The server follows basic MCP structure but lacks production-grade polish in output definition and error guidance.

• Add a 'Returns' section to each tool description documenting the output schema. Example: 'Returns: {seriess: [{id, title, units, frequency, seasonal_adjustment, observation_start, observation_end}]}' so LLMs know what fields to expect.
• Document result limits: 'search() returns up to 1000 results by default; pass limit=<N> to request fewer. Use orderBy and sortOrder to control ordering for pagination.' Add a note: 'For very large result sets, consider narrowing search_text or adding tag filters.'
• Enhance error handling in both tool handlers. Catch specific error codes (e.g. 404 for missing series, 401 for bad API key, 429 for rate limit) and return structured, actionable errors. Example: `{error: 'Not Found', message: 'Series XYZ not found. Verify the series ID with search().', retryable: false}`
• Annotate both tools as read-only in their definitions. In src/index.ts, when registering tools, add `toolUseWarning: 'readOnly'` or equivalent annotation.
• Add a 'Discovery' section to each parameter description where enum values are non-obvious. For 'frequency' parameter in series(), clarify: 'Frequency code (d=daily, w=weekly, bw=biweekly, m=monthly, q=quarterly, sa=semiannual, a=annual). Omit to use the series native frequency.'
• Document tag discovery: 'For tagNames/excludeTagNames, common tags include: 'nsa' (not seasonally adjusted), 'bls', 'quarterly'. Use search results to see available tags for each series.'
• Add validation to handler functions: validate seriesId format (typically uppercase alphanumeric), validate dates in YYYY-MM-DD format, validate limit/offset are positive. Return clear constraint violation messages.