PubMed MCP demonstrates solid tool design with comprehensive parameter coverage and detailed descriptions. All 4 tools are explicitly registered with clear names, descriptions, and input schemas. However, there are gaps in output schema documentation, error handling guidance, and some parameter definitions lack actionable constraints. The naming is verb-focused and appropriate (search, fetch, summary), and descriptions are substantive (150-350 chars for tools, 50-150 chars for most parameters). Schema definitions use proper JSON Schema with types. Critical weakness: no documented output schemas for any tool, limiting LLM planning for chained calls. Error handling is minimal, no guidance on recovery steps, retryability, or how to handle malformed inputs.

• Document output schema for each tool. For pubmed_search and pubmed_advanced_search, specify: returns list of result objects with fields [pmid, title, authors, journal, pub_date, doi, ...]. For pubmed_fetch and pubmed_summary, document which fields are included in each variant (e.g. fetch includes full abstract, summary omits it).
• Convert parameter value lists to JSON Schema enums. For 'language', define as {"enum": ["english", "chinese", "french", ...]}. This prevents LLM hallucination and enables validation at the server level.
• Add format and pattern constraints to date parameters. For 'date_from' and 'date_to', add `"pattern": "^(\\d{4}(/\\d{2})?(/\\d{2})?)$"` and description: 'ISO-like format: YYYY, YYYY/MM, or YYYY/MM/DD (e.g., 2020, 2020/01, 2020/01/15).'
• Add min/max constraints to numeric parameters. For 'max_results', add `"minimum": 1, "maximum": 100` in schema and update description to: 'Maximum number of results to return. Must be between 1 and 100 (default: 10).'
• Document error scenarios and recovery paths. Add to tool descriptions: 'If the query is malformed, returns error with suggestion to use simpler keywords or advanced_search tool. If no results match, returns empty list. If PubMed API is unavailable, returns retryable error after 30s.'
• Remove example IDs and literals from descriptions. Change 'e.g., cancer AND immunotherapy' to just describe the syntax. Change 'e.g., 12345678' in pmids to 'numeric PubMed IDs only.'
• For 'pmids' parameter, either: (a) change type to array of integers/strings and accept ["12345", "67890"], or (b) validate comma-separated string strictly and document that spaces/other delimiters are not accepted.