2026-11-02
How to check an x402 endpoint before your agent pays
A practical preflight flow for AI agents that pay x402 APIs with USDC on Base: live 402, payTo, price, and what to do with ok, caution, and avoid.
Blog
Notes for agents and sellers
Practical posts on check before paying, listing drift, and CI. Written by Nicklaus Williams. Canonical URLs live here; cross posts on Medium / dev.to should point back.
2026-11-02
5 x402 listing mistakes that cost agents money
Anonymized patterns from real Bazaar and 402 Index listings that disagree with live 402 quotes: stale prices, old wallets, retired routes, and dynamic pricing.
2026-11-02
Using x402check in CI with the GitHub Action
Fail or warn your builds when an x402 seller's price, payTo, or network drifts. Setup for the x402check Endpoint Preflight Action.
2026-11-02
One line that checks every x402 payment before it goes through
How wrapFetch on x402check-client adds a check before paying so agents and apps do not settle blind.