mcp-probe-cli

MCP server conformance tester — zero external dependencies.

Catch spec violations before your MCP server ships. mcp-conform runs a suite of Model Context Protocol conformance checks and tells you exactly what's wrong and why.

pip install mcp-conform
mcp-conform server --transport stdio --command "python my_server.py"

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Why mcp-conform?

The official MCP Inspector accepts invalid JSON Schema that MCP clients (including Claude Code) reject — silently, with no useful error messages. You discover the problem when a real user reports it. mcp-conform catches it before push.

What it checks:

Check	What it validates
JSON-RPC envelope	jsonrpc: "2.0", matching id, exactly one of result/error
Initialize response	protocolVersion, capabilities object, serverInfo.name/version
tools/list structure	tools array, each tool's name/description/inputSchema
JSON Schema validity	Detects true/false boolean schemas rejected by Claude Code
Error responses	code (integer) + message (string) per spec
Method not found	Returns -32601 for unknown methods

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Usage

stdio transport (most common)

mcp-conform server --transport stdio --command "python my_server.py"
mcp-conform server --transport stdio --command "node dist/server.js"
mcp-conform server --transport stdio --command "uv run python -m mypackage.server"

HTTP transport

mcp-conform server --transport http --url http://localhost:8080

CI / GitHub Actions

# Fails with exit code 1 if any check fails
mcp-conform server --transport stdio --command "python my_server.py" --format json | tee report.json

# .github/workflows/mcp-conformance.yml
- name: Run MCP conformance checks
  run: |
    pip install mcp-conform
    mcp-conform server --transport stdio --command "python my_server.py"

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Output example

════════════════════════════════════════════════════════════
  mcp-conform report
  Server : python my_server.py
  Transport: stdio
  Duration : 312 ms
════════════════════════════════════════════════════════════

  ✓  jsonrpc_envelope
       JSON-RPC 2.0 envelope is valid
  ✓  protocol_version
       protocolVersion '2025-03-26' is valid
  ✓  capabilities
       capabilities is an object
  ✓  server_info_name
       serverInfo.name = 'MyServer'
  ✗  tool[0](search)_input_schema
       inputSchema invalid: JSON Schema 'true' literal is not accepted by Claude Code

────────────────────────────────────────────────────────────
  Result: FAIL  — 1/5 checks failed

  Failing checks:
    ✗  tool[0](search)_input_schema: inputSchema invalid: ...
════════════════════════════════════════════════════════════

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Zero dependencies

mcp-conform uses only Python stdlib (Python 3.10+). No mcp SDK, no httpx, no pydantic — nothing to install, no version conflicts.

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License

MIT