What is x402? HTTP 402 payments for AI agents

The direct answer

x402 is an HTTP payment pattern in which a service can respond with 402 Payment Required and a machine-readable way to satisfy the request. It lets compatible software pay for a specific resource or action without turning every call into a human checkout. A protocol response is not itself proof that a later business outcome occurred.

For x402 protocol, choose one question that a reviewer can answer from the record. Name the tool or source, the exact action, and the expected output before doing the work. This makes it easier to see whether the result actually answers the question or merely sounds plausible.

A practical way to apply this

1. Write the user's intended outcome in one sentence.
2. Identify which source, MCP tool, platform log, or human review can answer the question.
3. Run the smallest safe action and preserve its returned status, timestamp, and receipt link.
4. Check the receipt independently and label any evidence that is missing or outside the captured boundary.

A disciplined review separates the request, the tool execution, the saved result, and any later outcome. Ask what the system actually observed, then inspect the public receipt and its verifier. If the work changed another service, query that service directly or follow its confirmation reference. If that evidence is absent, report the outcome as unknown rather than filling the gap with an assumption.

A concrete example

A real example is this public read-only BTC lookup receipt: https://zambo.dev/run/83ae4fd7-b9f8-497c-b842-72381c8ee6a8. Its verifier is https://zambo.dev/api/v2/receipt/83ae4fd7-b9f8-497c-b842-72381c8ee6a8/verify. The example shows one observed tool result; it is not evidence about x402 protocol in your own system.

For a work-specific review, replace the sample with the receipt generated by your own call. Match the tool name and receipt ID exactly. If the output is a proposal, a blocked action, or an unavailable response, retain that state instead of describing it as completed work.

What the record can and cannot tell you

The useful distinction is between a payment challenge, a valid settlement, and the requested service result. Verify each stage against its own response: the challenge states terms, settlement evidence records payment, and a tool receipt records the service response. Do not treat one stage as proof of the next.

A checkable receipt records what the connected execution service saved. It does not establish that a model's complete answer is accurate, that every possible input was tested, or that an outside service changed state. When an outside effect matters, look for a confirmation from the system that owns that state, such as a read-back, callback, or provider reference.

For sensitive work, publish only the fields needed for review. Keep access tokens, private credentials, customer data, and unrelated chat context out of a public handoff. Explain what the receipt covers and what remains outside its scope.

Review checklist

• Does the record identify the specific request and tool?
• Does the receipt ID match the result being discussed?
• Can a reviewer reach the verifier without the original chat?
• Are failures, retries, and pending steps represented honestly?
• Is outside confirmation linked to its actual source?
• Are private values excluded from the public copy?

Use this checklist for what is x402? http 402 payments for ai agents and save only the evidence relevant to the decision. A short, well-scoped record is easier to review than a large transcript with no clear boundary.