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Version: 0.16.5

MCP-003: Invalid JSON Schema - MCP

Summary​

  • Rule ID: MCP-003
  • Severity: HIGH
  • Category: MCP
  • Normative Level: MUST
  • Auto-Fix: No
  • Verified On: 2026-02-13

Applicability​

  • Tool: all
  • Version Range: unspecified
  • Spec Revision: 2025-11-25

Evidence Sources​

Test Coverage Metadata​

  • Unit tests: true
  • Fixture tests: true
  • E2E tests: false

Examples​

The following examples demonstrate what triggers this rule and how to fix it.

Invalid​

{
  "name": "search",
  "description": "Searches for files matching a query string",
  "inputSchema": {
    "type": "invalid_type"
  },
  "outputSchema": {
    "type": 42
  }
}

Valid​

{
  "name": "search",
  "description": "Searches for files matching a query string",
  "inputSchema": {
    "type": "object",
    "properties": {
      "query": { "type": "string" }
    }
  },
  "outputSchema": {
    "$schema": "https://json-schema.org/draft/2020-12/schema",
    "type": "object"
  }
}