What Is x402 Protocol? Open Payments for AI Agents

x402 is an open payment protocol for the web that activates the long-dormant HTTP 402 "Payment Required" status code. It defines a machine-readable handshake: when a client requests a paid resource, the server answers with a 402 response stating the price and the payment terms; the client attaches a payment, typically a USDC transfer on a low-cost blockchain, and retries; the server confirms that the payment has settled and returns the resource. The result is pay-per-request access over plain HTTP, with no accounts, no API keys, and no subscriptions.

The protocol was designed for a web where the buyer is increasingly a piece of software. An AI agent that needs a market-data point, a search result, or a generated image can discover an x402 endpoint, read its price, pay it, and consume the response inside a single HTTP exchange. There is no signup form to complete, no billing dashboard to configure, and no human required on either side of the transaction.

Who created x402?

x402 originated at Coinbase, which released it as an open protocol rather than a proprietary product. The design goal was to give the internet a native payment layer that any server, client, or payment infrastructure provider could implement without permission. Because the specification is open, the ecosystem around it is not controlled by a single vendor: independent facilitators, client libraries, and service operators all participate. This directory exists to make that ecosystem legible — every service listed here accepts x402 payments from arbitrary clients, including autonomous agents that no one has manually onboarded.

The problem x402 solves

Traditional web monetization assumes a human customer. Signup flows, credit-card forms, invoicing cycles, and API-key provisioning all presume a person who can pass identity checks, store credentials, and manage an ongoing billing relationship. An autonomous agent can do none of these things: it cannot complete a card checkout, sit through a KYC review, or juggle logins across fifty vendors. Even where automation could fake the paperwork, the economics fail, because card networks charge fixed per-transaction fees that make a one-cent purchase irrational for buyer and seller alike.

x402 removes both frictions at once. Authentication collapses into payment: the client's wallet signature is the only credential the server ever inspects, so there is no account database to maintain and no API key to leak or rotate. And because settlement happens in stablecoins on low-fee networks, prices the card world cannot express — a tenth of a cent, a thousandth of a cent — become routine. Agents get a uniform way to buy, sellers get a uniform way to charge, and neither side needs a prior relationship with the other.

Stablecoin micropayments as the payment rail

In x402, the unit of account is a stablecoin, in practice USDC, and settlement happens on-chain. Two networks dominate the listings in this directory: Base, an Ethereum layer-2 network, and Solana, a high-throughput layer-1. Between the client and the server sits a facilitator, a service that verifies the payment payload and settles the transfer so that neither side has to operate blockchain infrastructure of its own.

Because the marginal cost of moving a small amount of USDC is minimal, genuinely tiny prices work. The most common price band in the directory is micro — $0.01 or less per request, and listed prices run from $0.00001, a thousandth of a cent, up to $10 for a single call. Every listing in the directory prices per request and accepts USDC.

The ecosystem in this directory

x402 Looker indexes 100 x402-enabled services. The heaviest concentration is in finance and trading (60 listings) and data APIs (21), with MCP tools, search and retrieval, media generation, commerce, and content paywalls making up the remainder. By chain, Base accounts for 87 listings against 13 on Solana. Settlement is handled by seven facilitators; the Coinbase facilitator clears the large majority, with payai, codenut, dexter, corbits, daydreams, and mogami serving the rest.

What you can buy with x402

The catalog is already varied. Market data, trading signals, and analytics aimed at autonomous trading agents form the largest group. Structured data APIs sell everything from address lookups to token metrics by the call. Search and retrieval endpoints return ranked results or cleaned documents per query, media generation services sell images and other output per generation, and content paywalls unlock individual articles or reports for a micropayment. Hosted MCP tools charge agents for each tool call, which makes x402 a natural payment layer for tool-using agent frameworks.

What x402 is not

A few boundaries sharpen the definition. x402 is not a blockchain and not a token: it is a messaging convention layered on HTTP that uses existing chains for settlement. It is not a payment processor or custodian: funds move from the client's wallet to the server's address, with the facilitator only verifying and broadcasting the transfer. And it is not a subscription system: the protocol knows only discrete, paid requests, so there is no recurring-billing state to manage on either side.

Browse the x402 Looker directory to see the protocol in production, or start with the short x402 explainer for a two-minute overview.