x402 Domain & Nonce Window Checker

Checks an EIP-3009 TransferWithAuthorization's domain separation and replay-defense-adjacent fields against caller-supplied expectations. expected_chain_id and expected_verifying_contract are mandatory policy parameters, separate from the chainId/verifyingContract actually baked into the signed domain -- a mismatch on either is a hard refuse, never a soft warning (the cross-domain replay defect EIP-712 domain separation exists to prevent). Also checks the validAfter/validBefore window against a caller-supplied now_unix, and the nonce's format (bytes32, non-zero). Accepts an optional caller-supplied nonce_already_used boolean; this kernel never queries a chain -- on-chain nonce uniqueness is enforced by the token contract at settlement time, not by this verifier. Zero network calls; never a facilitator, proxy, or settlement relay.

Tool URL: https://ainumbers.co/chaingraph/art-592-x402-domain-nonce-window-checker.html