I wrote a book about the part of x402 nobody shows you: the actual bytes. I built a paid API on a Cloudflare Worker and measured the whole path — the 402 challenge, the payment, and the 200 delivery — and I kept every response.
Free to read (3 of 9 chapters): what a 402 PAYMENT-REQUIRED really contains — the v2 header form and the v1 body form, field by field, plus how to inspect your own 402 without paying anything.
The paid chapters (4–9) cover the build: the Worker implementation, putting v1 and v2 in the same 402, the pitfalls that cost me hours (including what facilitator /verify demands of the payer's balance), gasless EIP-3009 settlement, listing in catalogues (402index / x402scan / OpenAPI), and measuring traffic by splitting 402 (interest) from 200 (delivery) in Cloudflare GraphQL Analytics.
Every number in the book is measured, with the response, the milliseconds, the tx hash and the KV key.
The book (Japanese) — 500 JPY, first 3 chapters free: https://zenn.dev/noboru_x402/books/0b07438ec3a454
Top comments (0)