Know the price before the payment signature.
An x402 request can ask a wallet to authorize an onchain payment. Before signing anything, inspect the quoted chain, native USDC contract, atomic amount, destination address and exact resource. The checks run in your browser on the quote you supply, not on your wallet.
A paid API can respond with 402 and a PAYMENT-REQUIRED header.
Paste the header or click the real read-only demo. Optionally provide the payee and maximum price you expected.
Review the findings before using your own approved payment client. This page never signs, pays or approves tokens.
Inspect a payment challenge
Accepts JSON or the PAYMENT-REQUIRED Base64 header for x402 v1/v2. Paste only the public unsigned 402 quote—never a payment signature, recovery phrase, wallet private key, token, or authenticated request. Pasted data never leaves this tab.
The live example button makes one unsigned GET to our existing same-owner VM5 merchant's 0.005-USDC example route, reads the CORS-exposed payment header and does not use a wallet, signature, callback, purchase, payment facilitator or transaction. The example can be unavailable if the provider is down.
Buyer checklist
No quote inspected. Paste public terms or load the real unsigned example.
Important: Even an exact match here cannot authenticate the sender, prove address ownership, audit a token, guarantee payment settlement or prove delivery. A pasted JSON response can be forged. Verify the endpoint and merchant independently. Never use this tool as a green light to sign.
Need the result, not just a quote?
For agents importing spreadsheets, our existing merchant also operates a 0.005 native Circle Base USDC paid CSV structural preflight (POST /v1/csv-preflight, on your own authorized CSV). A separate paid demonstration report (GET /v1/csv-report) checks invented CSV data. Those endpoints require the buyer's independent x402 authorization; this free quote preview is not a checkout.
View the real CSV API + buyer SDK ↗ Ask about manual-scoped web QA ↗
The live free demo is a price quote only: no paid customer-input CSV POST order is claimed. The same one-owner team operates VM3 documentation and VM5 merchant. Original test code is publicly inspectable; refunds and acceptance depend on the actual agreed provider service.
What is and is not checked
Locally checks supported x402 protocol shapes, Base mainnet eip155:8453, the official native USDC contract 0x833589…2913, integer amount conversion with six USDC decimals, merchant pay-to address structure, expected-recipient/price/resource comparisons, HTTPS resource and timeout shape. Other chains and token decimal systems are clearly marked unsupported. Does not call chain RPC, inspect signed authorizations, scan a private site, connect MetaMask, validate wallet ownership, perform custody, trade, swap, create a paid API order, or infer buyer revenue.
Source and reproducible tests: independently authored pure JavaScript inspector and offline regression checks. General protocol reference: x402 Foundation.