ART-26 · Branch B · Agentic Rail Chain · OpenChainGraph

x402 Header Decoder, Payload Linter & 402 Flow Simulator

x402 turns the dormant HTTP 402 Payment Required status into a stablecoin paywall settled by a facilitator. This workbench decodes the base64 PAYMENT-REQUIRED / PAYMENT-SIGNATURE / PAYMENT-RESPONSE headers, lints an exact-scheme PaymentPayload, walks the request → /verify → /settle flow, and shows which scheme×network pairs are live. Produces a §4 compliance_control OpenChainGraph artifact.

⚠ x402 is an evolving Linux Foundation project. The exact-scheme sub-fields are illustrative (EIP-3009 style) — confirm field names against the x402 spec before building. Nothing here touches a chain or facilitator.

§4 OpenChainGraph · ART-26 x402 · exact scheme Zero PII Client-Side · No Network

▸ Decode an x402 header value

Paste a base64 header value (with or without the PAYMENT-REQUIRED: / PAYMENT-SIGNATURE: / PAYMENT-RESPONSE: prefix). Decoded and pretty-printed locally.

▸ Lint an exact-scheme PaymentPayload

Paste a decoded PaymentPayload JSON. Top-level shape is checked; exact-EVM authorization sub-fields are validated as illustrative (EIP-3009 style).

▸ Walk the HTTP-402 flow

A deterministic walkthrough of the request → 402 → sign → re-request → verify → settle → 200 sequence with example objects.

▸ Scheme × Network support (Jun 2026 snapshot)

Which (scheme, network) pairs the Coinbase-hosted facilitator supported as of mid-2026. Verify current support against x402.org.