MCP tool linter.

The rules

Names

• MCP: 1 to 128 characters of letters, digits, _, - and ., unique within the server.
• Claude (Anthropic API) does not allow dots: ^[a-zA-Z0-9_-]{1,128}$. The Claude connector directory asks for names of at most 64 characters.
• Prefer verb-first, namespaced names such as orders_search over search.

Descriptions

• Every tool needs one. Anthropic recommends several sentences: what it does, when to use it and when not, and what each parameter means.
• Every parameter should have a description too.

Input schema

• The root must be {"type": "object"}. A tool without parameters should still send an object schema.
• Every name in required must exist in properties.
• For OpenAI strict mode: additionalProperties: false on every object and every property listed in required; avoid allOf, not and if/then/else.
• Gemini accepts a subset of OpenAPI 3.0 schema; keywords such as $ref, allOf, oneOf and additionalProperties may be rejected or ignored.

Annotations

• Without annotations, MCP clients must assume a tool is destructive and open-world.
• The Claude directory asks for a title and the applicable readOnlyHint or destructiveHint. ChatGPT app submissions ask for explicit readOnlyHint, destructiveHint and openWorldHint on every tool.

Tool count

• Selection gets worse with many tools. OpenAI suggests staying under 20, Google 10 to 20, and Anthropic sees accuracy degrade past 30 to 50.

Hosting the server? Run the live URL through the MCP server checker.