Single tool 'count_letters' has a clear, action-verb name and reasonable description (67 chars). Input schema is well-formed with proper types and per-parameter descriptions. However, output schema is documented only in the Elysia route definition (response: t.Object(...)), not exposed in the MCP tool registration itself. The tool is READ_ONLY and simple, but lacks error handling guidance, output field descriptions in the MCP context, and any indication of edge cases (empty word, no matching letters). The plugin auto-discovers routes marked with 'mcp: true' detail, which is clever but means tool definitions are split between Elysia metadata and MCP registration, harder to audit and maintain.

• Add output schema documentation to the MCP tool definition. Include field names, types, and descriptions for word, letters, total, and matches array. This enables LLMs to plan downstream operations.
• Enhance tool description with error handling guidance: 'Returns empty matches array if no letters match. Handles empty word or letters gracefully.'
• Add tool annotations: set readOnlyHint: true in the MCP tool definition to formally declare the tool is safe and idempotent.
• Centralize tool metadata in a dedicated MCP schema file or configuration, separate from Elysia route definitions. This improves auditability and reduces duplication.
• Add parameter constraints: document that 'word' and 'letters' should be non-empty strings, and explain behavior if they are empty.