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. See also: how x402 fields map to AgentCore Payments, VPSF/STARK, ACP, and MPP.

⚠ 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.

Ask your agent

Copy this paragraph into Claude, OpenClaw, or any MCP-aware agent to run this exact tool, with this sample, and verify the artifact.

Run the AINumbers MCP tool `simulate_x402_flow`. Task: Decode base64 PAYMENT-REQUIRED / PAYMENT-SIGNATURE / PAYMENT-RESPONSE headers, lints exact-scheme PaymentPayload (EIP-3009 style authorization fields), walks the HTTP-402 request/verify/settle flow, shows scheme×network matrix.
Call it with arguments: {"policy_parameters":{"header_or_payload":"{\"scheme\":\"exact\",\"network\":\"base-sepolia\",\"payload\":{\"signature\":\"0xabc123\"}}"}}
Verify before trusting: call `verify_execution_hash` on mcp.ainumbers.co (https://mcp.ainumbers.co/mcp) with the parameter `claimed_hash` set to the returned `execution_hash`, passing the full artifact the run returned (the object containing `policy_parameters` + `output_payload` + `execution_hash`; equivalently `policy_parameters` + `output_payload` with `claimed_hash`), not the bare hash string.
Return the ledger link https://ledger.ainumbers.co/ so a human can re-verify without contacting us.
PII rule: All inputs are processed locally in your browser. No data is transmitted. Do not enter real personal data — use synthetic or anonymised inputs only.
Open the tool with the sample prefilled: https://ainumbers.co/chaingraph/art-26-x402-payload-decoder-flow-simulator.html#p=v1.H4sIAAAAAAAA_wF0AIv_eyJoZWFkZXJfb3JfcGF5bG9hZCI6IntcInNjaGVtZVwiOlwiZXhhY3RcIixcIm5ldHdvcmtcIjpcImJhc2Utc2Vwb2xpYVwiLFwicGF5bG9hZFwiOntcInNpZ25hdHVyZVwiOlwiMHhhYmMxMjNcIn19In1M1RfhdAAAAA