OpenPredicate MCP Server demonstrates strong definition quality with one well-designed tool. The search_pets tool has a descriptive name, a comprehensive description (245 chars), and a properly structured input schema with inline filter schema and documented limit parameter. The tool description clearly explains what it does, when to use it, and what to expect. However, the server provides no documented output schema, no error handling guidance, and no tool annotations (readOnlyHint, destructiveHint). The filter schema validation is implemented server-side with error reporting, but the response format is not formally documented for the LLM. The tool is READ_ONLY by declaration but lacks proper schema annotations. With only one tool, strengths are concentrated but scope is minimal.

• Document the output schema formally. Add to SEARCH_PETS definition: outputSchema: { type: 'object', properties: { records: { type: 'array', items: { type: 'object', properties: { id, name, species, breed, age, ... }, required: [...] } }, total: { type: 'integer', description: 'Total matching records (for pagination awareness)' } }, required: ['records'] }
• Add tool annotations to inputSchema. Include readOnlyHint: true since search never modifies state. Add idempotentHint: true since identical calls return identical results (supports agent retry safety).
• Enhance error responses with recovery hints. When returning a validation error, include available queryable fields or valid operators. Example: { error: { type: 'unknown-field', message: '"age_years" is not queryable', pointer: '/filter/age_years', availableFields: ['age', 'species', 'breed', 'name'] } }
• Clarify pagination in limit parameter description. Change to: 'Maximum number of records to return (default 20, max 50). Results are truncated; if more matching records exist, call again with an offset or cursor-based parameter.' (Note: current implementation lacks cursor support, consider adding offset parameter or documenting limitation.)
• Add per-item success/failure detail. If filter matches 1000 pets but limit=20, return { records: [...], total: 1000, hasMore: true } so LLM knows pagination is needed, per mxe:enforce-result-limits.