Apple Health MCP has three well-defined tools with clear schemas and reasonable descriptions. All tools are READ_ONLY and have proper input schema validation via AJV. Tool names follow verb_object conventions (health_query, health_report, health_schema). Descriptions are present and informative (94-162 chars), exceeding the 10-char minimum. However, there are notable gaps: (1) no output schema documentation, LLMs cannot infer the structure of results, only that query returns 'json', 'csv', or 'summary' format, (2) no detailed parameter descriptions explaining constraints (e.g., what constitutes a valid DuckDB query, what metrics are available for include_metrics array), (3) no error handling guidance, if a malformed query is passed, the tool provides no recovery hints, (4) no per-parameter validation messages, (5) tool composition lacks reference IDs in responses that downstream tools might need. The health_schema tool is well-positioned as a discovery mechanism but lacks explicit guidance ('Call this first to understand available tables'). Parameter schemas are properly typed (string enums for format/report_type) but lack minLength/maxLength or pattern constraints on free-form inputs like 'query'. Error reporting is enabled but no evidence of custom recovery messages.

• Document output schema for health_query: 'Returns an object with keys: data (array of records), count (total rows), duration_ms (query time). For format=summary, returns {summary: string, data: array}.'
• Document output schema for health_report: 'Returns {report_type: string, period: {start: ISO8601, end: ISO8601}, metrics: object with metric names as keys and values as numbers/strings, generated_at: ISO8601}.'
• Add constraint to health_query 'query' parameter: minimum 5 characters, pattern for basic SQL validation, and guidance: 'Must be a valid DuckDB SELECT query. Available tables: [listed from schema]. Joins and window functions supported.'
• Replace health_report 'include_metrics' description with enum or explicit list: 'Array of metric names to include. Valid values: sleep, workouts, steps, heart_rate, stress, mindfulness. Omit to include all.'
• Add error handling guidance to tool descriptions: 'On error, will return a clear message like: "Invalid query: table 'workouts' not found. Available tables: [list]. See health_schema for details."'
• Update health_schema description to indicate discovery role: 'Returns the schema of all available Apple Health tables, their columns, units, sample rows, and query tips. Call this first to understand the data structure before using health_query.'
• Add per-parameter descriptions and examples to health_report: 'start_date and end_date are ISO 8601 dates (YYYY-MM-DD format). For weekly reports, dates are optional and default to the current week. For custom reports, both are required.'