x402 Conformance MCP server

x402 Conformance

Prove your x402 payments can't double-credit, credit too early or credit on a broken answer, in one CI step.

An open set of conformance and safety checks for x402 facilitators and resource servers. It checks the properties a seller's money depends on. It never signs, pays or touches mainnet. It complements x402 and its facilitators and doesn't replace them.

Experimental. Passing a check is evidence about one property. It doesn't certify conformance to x402. — Ryan Gillespie, Optitransfer

Project page with the checks and the latest results: https://atsp-protocol.github.io/x402-conformance/ Release map: RELEASES.md. What the suite covers, check by check: docs/COVERAGE.md.

60-second quickstart

See it work first, with nothing to set up: no project, no wallet, no chain, a few seconds each.

npx -y x402-conformance-svm demo                       # R0-R10 against a bundled mock server behind a facilitator double
pipx run --spec x402-conformance x402conf demo         # S1-S4, P1-P7 against a bundled mock, then the F1-F12 and S5 self-test
npx -y x402-conformance-svm demo --fault serve_on_any_settle   # what a failure looks like, with a fix link per check

Then point it at your own code:

pipx run --spec x402-conformance x402conf live https://x402.org/facilitator        # a facilitator's GET /supported
pipx run --spec x402-conformance x402conf resource https://your.api/paid-route      # your 402 answer, one unpaid GET
npx -y x402-conformance-svm probe --resource http://127.0.0.1:4020/paid --start "node server.js"   # fault injection

In CI, save this as .github/workflows/x402-conformance.yml:

name: x402 conformance
on: [push, pull_request]
jobs:
  x402:
    runs-on: ubuntu-latest
    steps:
      - uses: actions/checkout@v4
      - uses: atsp-protocol/x402-conformance@v1
        with:
          resource-url: http://127.0.0.1:4020/paid   # your paid route
          start: node server.js                      # must use X402_FACILITATOR_URL as its facilitator

From your test suite, agent or CI system: docs/USING.md covers vitest, jest, node:test, Hono, Express, pytest (FastAPI, Flask), MCP clients (Claude, Cursor), the Vercel AI SDK, LangChain, Docker and GitLab CI, with the same checks and report everywhere. Failures you choose to share build the public corpus of real x402 failures.

Who should use this

Shortened. The full README is on GitHub.