Python Code Validator MCP Server

Python Code Validator

A hosted service that checks AI-generated Python before it ships: syntax and lint diagnostics, an AST security policy that also catches calls hidden behind dynamic imports and runtime attribute lookups, a bandit pass, a credential scan and deterministic repair — one verdict with a score.

This repository holds the client side: the MCP configuration, the CI script and the pre-commit hook. The service itself runs at https://api.statemind.ai, so there is nothing to install or host.

A key, without an account

curl -s -X POST https://api.statemind.ai/v1/keys
# {"api_key": "msvc_free_…", "tier": "free", "calls_per_day": 100, "modes": ["static"]}

100 validations a day, metered per UTC day. Every answer carries the state of the allowance (x-quota-remaining, x-quota-reset), so a client can back off before it is cut off.

MCP

Registered in the official MCP registry as ai.statemind/python-code-validator, a name verified against the domain that serves it rather than a GitHub account. Any MCP client adds it with one block:

{
  "mcpServers": {
    "python-code-validator": {
      "type": "http",
      "url": "https://api.statemind.ai/mcp",
      "headers": { "Authorization": "Bearer msvc_free_…" }
    }
  }
}

• Claude Code: claude mcp add --transport http python-code-validator https://api.statemind.ai/mcp --header "Authorization: Bearer msvc_free_…"
• Cursor: ~/.cursor/mcp.json, same block.
• VS Code / Copilot: .vscode/mcp.json under "servers".

A client that only launches a command uses the stdio bridge in this repository instead, which forwards the same tool over HTTPS:

{
  "mcpServers": {
    "python-code-validator": {
      "command": "python3",
      "args": ["/path/to/python-code-validator/mcp_stdio.py"]
    }
  }
}

Or as a container, which the Dockerfile here builds:

docker build -t python-code-validator .
docker run -i --rm -e VALIDATOR_API_KEY python-code-validator

Gemini CLI installs the same bridge as an extension, with the instruction file that makes it get used:

gemini extensions install jkanselaar/python-code-validator

Three tools, named after what they do to the code:

The old single python_code_validator tool, with its mode argument, still answers for clients that already configured it, but is no longer listed.

One line in a project's agent instructions is what makes an agent actually use any of it:

Validate every generated Python file with validate_python before presenting it. Do not present code the validator marks invalid.

CI

The service hands out the client, so a workflow needs no checkout of this repository and no secret:

- run: |
    curl -sf https://api.statemind.ai/v1/client -o validate.py
    python3 validate.py --changed-against "origin/${{ github.base_ref }}"

Or as an action:

- uses: jkanselaar/python-code-validator/.github/actions/validate-python@main
  with:
    api-key: ${{ secrets.VALIDATOR_API_KEY }}   # optional; free tier without it

The changed Python is validated and offending lines are annotated on the diff, failing the job on syntax errors and unsafe patterns. Files the service refuses outright (over its 200 kB limit) are skipped with a warning rather than failing the run.

Pre-commit

repos:
  - repo: https://github.com/jkanselaar/python-code-validator
    rev: v1.6.7
    hooks:
      - id: python-code-validator

The client itself

validate.py is standard library only, so it also works as python validate.py file.py in a Makefile, a git hook or a container:

$ python3 validate.py service.py
::error file=service.py,line=88,title=SyntaxError::invalid syntax
FAIL service.py score=0.66

0/1 files accepted

VALIDATOR_API_KEY is used when set; otherwise the client mints a free key. VALIDATOR_URL points it at another deployment.

HTTP

curl -s https://api.statemind.ai/v1/validate \
  -H "Authorization: Bearer $VALIDATOR_API_KEY" \
  -H 'content-type: application/json' \
  -d '{"code": "def f(:\n    pass\n", "mode": "static"}'

mode is static, repair or execute; repair and execute need a configured key. Submitted code is not logged.

A refused call says what to do about it, so a caller with no operator to ask can resolve it itself:

{"error": "payment_required",
 "remedy": {"action": "upgrade_key", "hint": "A free key covers static only. …"}}

Licence

MIT.