Does a 402 challenge prove payment?

No. An HTTP 402 quote only advertises terms. It is not a signature, a settled transaction, an authenticated provider, or accepted delivery.

Does this quote inspector send payment credentials to a server?

No. The inspector parses pasted data in the user's browser without making API requests, connecting a wallet, collecting a payment signature or submitting quote content.

Can this tool detect a wrong token, chain, recipient or excessive amount?

It checks quote fields against Base mainnet USDC, an optional expected payee, and an optional maximum budget. Those are format and consistency checks, not proof that a provider or receiver is trustworthy.

Free developer utility · inspect before spend · released October 26, 2026

See the x402 quote before an agent pays.

Paste an HTTP PAYMENT-REQUIRED header or JSON body. This inspector locally decodes each proposed payment and checks scheme, Base mainnet, USDC token, receiver address, and optional budget ceiling. It exposes mismatches without requesting a wallet connection or authorizing a cent.

No wallet connection. No API keys. No signing. No payment. No upload of your pasted quote. This tool checks fields; it does not authenticate the provider, verify on-chain settlement, or prove accepted delivery.

Free x402 Quote Inspector

All field evaluation happens locally in your browser. This module uses no network requests; the wider website may serve standard page analytics independently of this quote analyzer. Do not paste wallet private keys, signatures, bearer tokens, or customer secrets.

What counts as proof in an x402 payment?

1. Quote

HTTP 402 advertises amount, network, asset and payee. The inspector can validate structure and user-entered limits. It cannot establish payment.

2. Settlement

After caller-controlled authorization, verify actual chain transaction and the expected receiver, token, amount and confirmations from an independent chain source.

3. Accepted result

Verify that the requested work arrived, passed acceptance checks, and can be bound to the settlement record. Payment alone is not successful delivery.

How can an agent reproduce the no-spend check?

curl -i 'https://squeezeos-api.onrender.com/api/web/research/info'
# Readiness is free and is NOT a payment or delivery proof.
# For a paid target, request fresh terms without a PAYMENT-SIGNATURE.
# Paste its returned PAYMENT-REQUIRED header into the inspector above.

Research note: SCRIPTMASTERLABS published a dated, no-signature price challenge audit for six SML production jobs on September 6, 2026. It reported 6/6 displayed-price matches at that time, but no payment or customer activity. Read the original measurement and limitations or inspect its structured evidence. Its dated results are not today's live validation.

What can an independent developer audit?

The core decoder is inspectable: view the standalone JavaScript module and read adversarial test cases. It supports x402 v1 (network: base, maxAmountRequired) and v2 (network: eip155:8453, amount) accepts[] offers. Missing, conflicting, or cross-version fields are blocked, along with wrong tokens, payees, or budget overruns. Compare against the v1 specification and v2 specification. Any unsupported chain or token is blocked rather than silently accepted.

Download the reproducible fixture pack: 20 synthetic x402 safety cases (JSON) plus a Node test runner. This covers version mismatches, wrong payees/tokens/networks, budget limits and malicious mixed offers. None of the fixtures represents real paid traffic or third-party adoption.

Deliberate limits: no remote fetch, no provider authentication, no wallet, no customer telemetry, no off-chain exchange-rate conversion, no fee estimation, no multi-token price conversion, no external verification, and no guarantee the provider honors the price. A parseable quote remains an untrusted claim until checked.

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Frequently asked questions

Does a 402 challenge mean the AI agent has paid?

No. It only expresses a payment requirement. A signature, settled chain transaction and accepted output are separate proof states.

Can I inspect a quote before deciding to buy?

Yes. Paste the header locally and optionally enter a recipient address and spending ceiling you established independently. Do not interpret a structural pass as an endorsement or security audit.

What can I share with other developers?

Share this tool's canonical URL, the transparent audit methodology, and the open-source decoder. Quote content remains only in the reader's browser; do not publish customer-specific payment challenges without permission.