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x402

Pay x402 is an open, HTTP-native payment protocol that activates the long-reserved (since 1999) HTTP 402 "Payment Required" status code: a server responds 402 with machine-readable payment requirements, the client pays (in practice, stablecoins over an EVM-compatible network) and retries the request with proof of payment attached [1]. It solves instant, account-free, per-request monetization for APIs and agentic consumers — no signup, no KYC, no stored API keys, no prepaid credit balance — collapsing what the project calls a five-step "old way" of API onboarding into three HTTP round trips [own site, x402.org homepage].

Overview

It does not itself define a payment network; it is a wire-format and challenge/response convention that networks and asset issuers plug into via a scheme and network field (the reference implementation targets EVM chains and USDC, per the transport spec's example payload) [1]. Version 2 of the specification moved the payment-required and payment-signature payloads into dedicated PAYMENT-REQUIRED and PAYMENT-SIGNATURE HTTP headers rather than embedding them in earlier v1 conventions, and the specification separately defines non-HTTP transports (the repository lists transports-v1 and transports-v2 directories) [1].

As of this verification, x402 is governed by the x402 Foundation, described in its own site footer as "a Series of LF Projects, LLC" — i.e., a Linux Foundation-hosted project — with an operational launch announced by the Linux Foundation on 2026-07-14 [2]. Coinbase originated the protocol; the Foundation now governs it independently of any single company, per the project's own framing [x402.org homepage]. The site's homepage displays a real-time usage dashboard claiming 75.41M transactions and $24.24M in volume over the trailing 30 days, with 94.06K buyers and 22K sellers, current as of this check [3] — but this figure is self-reported by the Foundation running the protocol, not measured by an independent index, so it is recorded here as claimed rather than observed or measured. What remains open: no independently operated adoption index (e.g. a third-party "402 index") was located and fetched during this verification to cross-check the Foundation's own dashboard number.

Discovery and probe

HTTP 402 response carrying payment requirements in a header · none — signalled per-request via the 402 status code, not a fixed well-known path

GET {origin}/{paid-path}
parse:     HTTP 402 status with a base64-encoded PaymentRequired object in the PAYMENT-REQUIRED response header (x402 v2 HTTP transport)
on absent: A 200 or a 402 without a PAYMENT-REQUIRED header means this specific path is not (or no longer) gated by x402 v2 over HTTP; the same origin could still use x402 over the MCP or other transports, or the legacy v1 header shape, so the probe only rules out v2/HTTP on the probed path.

Not probed live: no-fixed-path. A 402 challenge appears only on a URL that charges; there is no fixed path to check.

History

Instances

Every instance with its source is listed on the instances page.

See also

References

  1. x402's HTTP transport spec defines the 402 challenge as HTTP 402 status with a PAYMENT-REQUIRED header carrying a base64-encoded PaymentRequired object, and the client retry as a PAYMENT-SIGNATURE header carrying a base64-encoded PaymentPayload. — https://raw.githubusercontent.com/x402-foundation/x402/main/specs/transports-v2/http.md VERIFIED
  2. x402.org's footer identifies the project as 'x402 a Series of LF Projects, LLC', confirming Linux Foundation stewardship, and its Announcements page states the Linux Foundation announced the operational launch of the x402 Foundation on July 14, 2026. — https://x402.org/announcement (2026-07-14) VERIFIED
  3. x402.org's homepage displays a live self-reported dashboard: 75.41M transactions and $24.24M volume in the last 30 days, 94.06K buyers and 22K sellers, at time of check. — https://x402.org (2026-09-06) VERIFIED

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