x402

Agent internet protocolOpen Source

Open HTTP payment protocol for agents and APIs

Overview

About x402

This summary uses submitted and public product material. Only source-mapped claims are documentation reviewed.

x402 is an Apache-licensed HTTP payment protocol that uses 402 Payment Required so clients and agents can discover payment terms and pay for digital resources programmatically.

So agents can…

Discover payment requirements directly from an HTTP response
Pay for APIs and digital services on a per-request basis
Use extensible payment schemes without conventional API-key billing

Listing decision

Why x402 is listed

x402 defines interoperable payment messages and roles at the network boundary between clients, resource servers, and facilitators, so it is an agent-internet protocol rather than a wallet, gateway, or agent runtime.

Before you choose

Fit and limitations

Best for

API and content providers that want accountless per-request or usage-capped payment flows, plus automated clients and agents that need to discover and pay for compatible machine-readable resources.

Known limitations

Adoption requires compatible client and server implementations, wallets, supported assets and networks, and either direct verification or a suitable facilitator. Production network coverage and requirements vary by facilitator, and implementers must handle keys, payment failure, settlement, refunds, taxes, compliance, and abuse controls outside the core protocol.

Not yet verified

The protocol and scheme set continue to evolve, and this review did not independently test cross-implementation interoperability, facilitator security, settlement reliability, adoption, or regulatory treatment.

Sources

Sources and verification

First-party unless marked otherwise. Each link supports only its adjacent claim.

x402 introduction — HTTP payment flow and use cases
x402 is documented as an open payment standard in which a service responds with HTTP 402 payment requirements, a client submits a payment payload, and the service verifies and settles directly or through a facilitator before returning the resource.
official documentation · accessed Sep 3, 2026
x402 v2 specification — protocol messages and transport scope
The v2 specification defines payment-required and payment-payload structures, scheme and network identifiers, resource metadata, extensions, and use across HTTP, MCP, A2A, and other request-response transports.
official specification · accessed Sep 3, 2026
x402 seller quickstart — SDKs, middleware, and facilitator setup
The seller guide documents TypeScript, Python, and Go packages plus middleware for several web frameworks, testnet facilitator configuration, wallet requirements, and fixed or usage-capped payment schemes.
official documentation · accessed Sep 3, 2026
x402 network support — facilitator-dependent deployment
The network guide distinguishes the testnet-only x402.org facilitator from third-party production facilitators and documents the option and prerequisites for running a facilitator independently.
official documentation · accessed Sep 3, 2026
x402 repository license — Apache 2.0
The maintained x402 specification and reference SDK repository is published under the Apache License 2.0.
official license · accessed Sep 3, 2026