AI & Agentic Systems

MCP tool-definition linter

Lint MCP or function-calling tool definitions for what fails silently — descriptions that don't say when to use a tool, undescribed parameters, missing safety annotations.

A model picks a tool by reading its description, and fills the arguments by reading the parameter descriptions. A definition written for a human — “Gets an order” — gives it nothing to decide when to call it. Nothing errors; the behaviour is just quietly wrong.

MCP tools array, or function-calling definitions

{
  "tools": [
    {
      "name": "get_order",
      "description": "Gets an order",
      "inputSchema": {
        "type": "object",
        "properties": { "orderId": { "type": "string" } },
        "required": ["orderId"]
      }
    },
    {
      "name": "fetch_order",
      "description": "Gets an order from the system",
      "inputSchema": {
        "type": "object",
        "properties": { "id": { "type": "string", "description": "The order identifier" } },
        "required": ["id"]
      }
    },
    {
      "name": "cancel_order",
      "description": "Cancels an order. Use this only when the user has explicitly confirmed the order number and understands the cancellation is final.",
      "inputSchema": {
        "type": "object",
        "properties": {
          "orderId": { "type": "string", "description": "The order to cancel" },
          "reason": { "type": "string" },
          "status": { "type": "string" }
        },
        "required": ["orderId", "notes"]
      }
    }
  ]
}

Tool definitions are an integration contract wearing new vocabulary — the same authentication, scope, validation and audit questions any interface has answered for twenty years. Why we think the work sits below the model.

Checks the things that fail silently: descriptions that say what a tool is but not when to use it, undescribed parameters that become hallucinated arguments, free-string fields that should be enums, write-like tools with no safety annotations, and near-duplicate descriptions that make selection arbitrary. Runs in your browser.

Other tools

These exist because the underlying problem is real. If the numbers you just put in look uncomfortable, that is usually worth a conversation.

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