The server demonstrates solid definition quality with 20 well-organized tools across 6 functional domains (index, document, cluster, alias, data stream, analyzer). All tools have names starting with action verbs (list_, get_, create_, delete_, search_, put_, index_, analyze_), descriptions ranging 20 - 100+ characters, and JSON Schema input parameters with type declarations. However, there are consistent gaps: (1) Output schemas are not documented in the code, the rubric requires documentation of return types, and inspection shows no explicit schema definitions for tool responses; (2) Many parameter descriptions are terse (10 - 30 chars), missing format/constraint details required by the pattern:constrained-input guideline; (3) Error handling guidance is absent, no recovery suggestions, no error classification (retryable vs. fatal), no examples of what LLMs should do on failure; (4) Destructive operations (delete_index, delete_document, delete_by_query, delete_alias, delete_data_stream) lack confirmation/dry-run safeguards. The naming is consistent and clear (verb_noun pattern), and all tools declare the 'cluster' parameter for multi-cluster support, which is a composition strength. But these omissions prevent a higher grade.

• Document return schemas for all 20 tools. For each tool, add a 'Returns' section in the tool description or in code comments specifying field names, types, and what each field means. E.g., 'Returns: {indices: [string], total_count: int, took_ms: int}'.
• Add confirmation/dry-run support to destructive operations. Implement an optional 'confirm' or 'dry_run' parameter (default false) on delete_index, delete_document, delete_by_query, delete_alias, delete_data_stream. Dry-run returns success/failure prediction without executing.
• Enhance parameter descriptions with constraints and formats. For 'size' params, specify min/max (e.g., '1 - 100, default 10'). For 'query', add example DSL format. For 'body', specify expected JSON structure. Use JSON Schema pattern and minLength/maxLength where supported.
• Add error handling guidance to tool descriptions. For each tool, add a sentence: 'If the resource does not exist, returns a 404 error. Verify the name/ID and try again or use list_* to discover available resources.' For destructive ops: 'Cannot be undone, ensure correct parameters before calling.'
• Cap and document pagination limits. State in list_documents, list_indices, search_documents: 'Maximum size: 100. For large result sets, use pagination with offset or cursor.' Implement server-side max limits.
• Clarify parameter relationships in analyze_text. Add to description: 'If index is specified, analyzer is derived from index settings unless overridden. If analyzer is provided, index is not needed. Tokenizer, filter, and char_filter are for custom analysis chains.'

Inferred effective spec: 2025-06-18+.

• Relies on Logging (deprecated) - log to stderr or use OpenTelemetry