vanilla-mcp is a minimal HTTP server with 4 tools for Sonos device control. All tools are explicitly registered with names, descriptions, and input schemas visible in Program.cs. However, the server has significant gaps in definition quality: (1) Parameter descriptions are minimal or absent, only 'id' and 'volume' are described; parameters like those in get_system_status and get_devices lack any description. (2) Output schemas are completely undocumented, there is no specification of what structure get_devices, get_device_volume, or set_device_volume return, forcing LLMs to guess. (3) Error handling is absent, there are no error messages guiding LLM recovery, and invalid inputs (e.g., non-existent device ID) return only a text string with no recovery guidance. (4) Tool descriptions are minimal (10-50 chars), below the production baseline of 194 chars, and lack context on when to use each tool or what they return. (5) No input validation or constraints, e.g., volume accepts any integer but the description mentions '0 - 100'; no enum or min/max constraint is enforced. (6) Composition is weak: get_device_volume and set_device_volume both accept 'id', but there's no documented mechanism for discovering valid device IDs without calling get_devices first. Tools average 1.5 parameters with minimal documentation, well below production norms.

• Document all output schemas in the tool description or via explicit schema field. Example: 'Returns: {"devices": [{"id": string, "name": string, "room": string, "model": string}], "total": number}'. This lets LLMs know exactly what to expect and plan downstream calls.
• Expand all tool descriptions to 100-200 characters. 'Checks the status of the system' should become 'Checks the operational status of the Sonos system, including network connectivity, CPU load, and active device count. Call this first to verify the system is responsive before controlling devices.'
• Add discovery hints to parameter descriptions: For 'id' in get_device_volume/set_device_volume, add 'Call get_devices() first to obtain valid device IDs.'
• Add JSON Schema constraints for numeric parameters. In set_device_volume's 'volume' property, add '"minimum": 0, "maximum": 100' to enforce the 0 - 100 range at the schema level, not just in description text.
• Implement structured error handling. Instead of returning plain text like 'No device found with id 1', return a structured error object: {"error": "device_not_found", "message": "Device with ID '1' not found", "available_ids": ["2", "3"], "recovery": "Call get_devices() to see available devices and retry with a valid ID"}.
• Add parameter descriptions for tools with empty parameter sets. For get_system_status and get_devices, document in the description: 'This tool takes no parameters.'
• Consider adding an optional 'device_name' parameter to get_device_volume and set_device_volume as an alternative to 'id', since users naturally say 'What is the Living Room volume?' rather than 'What is device 1's volume?'. This matches the chat data model and reduces lookup friction.