What an x402 marketplace is

An x402 marketplace is a catalogue an agent can search for free and pay against, one call at a time, in USDC. This page is that explanation for PayAPI Market.

Last updated: 12 November 2026

The short answer

An x402 marketplace is a public catalogue of APIs that a program can find and pay for one call at a time. The payment uses the x402 protocol: the server answers an unpaid request with HTTP 402, the client pays the amount in the challenge, and the server returns the product. PayAPI Market is one such marketplace. x402.org publishes the protocol. It is not itself a catalogue of APIs.

This page is the explainer. The product front door stays the homepage, whose title is "x402 marketplace for AI agents". The two pages do not share a title.

What x402 is

HTTP status 402 has meant Payment Required since the early HTTP specifications. For years it was reserved and unused. x402 is the open protocol that puts a stablecoin payment on that status. A server that speaks it does not ask the caller to create an account, paste an API key, or buy a monthly plan. It names a price, a receiving wallet, an asset and a network, and it waits for a signed payment for that exact call.

On the networks PayAPI Market listings use, the asset is USDC. Base (eip155:8453) is the network every listing can settle. A listing can also accept Solana or Algorand when the provider offers that rail. The challenge is the contract. If the amount, the wallet or the asset is not what you expect, the client should not sign.

A marketplace sits beside the protocol. It does not replace it. The marketplace's job is discovery and, on PayAPI Market, a paid check of specific routes. The provider's server still does the selling. PayAPI is not in the payment path of a buyer's call. The USDC goes from the buyer's wallet to the provider's wallet through the provider's facilitator. Listing is free, and PayAPI takes 0% of each job.

How buying works over MCP

MCP, the Model Context Protocol, is how an agent client such as Claude Desktop, Cursor or a custom agent lists tools on a server. PayAPI's catalogue server is https://payapi.market/mcp. It is free to call. The tools are search_apis, list_apis, get_api, search_agents and submit_listing. The four read tools do not settle a payment. submit_listing is also free: it sends a URL and a contact email into review, and it never marks a listing settlement-verified by itself.

A typical purchase has two hops. First the agent asks the catalogue, over MCP, for a listing that matches the job. The catalogue returns the provider's URL, the price range, the category and whether a route is settlement-verified. That hop costs nothing. Second, the agent calls the provider's own URL. That is the hop that can return HTTP 402. The catalogue cannot spend the agent's money, because the payment is attached to the provider's request, not to the search.

You can paste the same MCP URL into a client config and skip the website. The human pages exist so a person can read the same facts the agent reads. The agents page shows the config block. How an agent finds PayAPI walks the HTTP twins of those tools: /agent/search, /agent/list, /agent/get and /openapi.json.

How buying works over HTTP

An agent that cannot speak MCP can do the same purchase with ordinary HTTP. Search is GET https://payapi.market/agent/search with a q parameter. The default list is the settlement-verified set. Adding verified_only=false includes listings that are live but have not been paid for yet. GET /agent/get?id= plus the listing slug returns one record, including verified_routes when a route has a receipt.

The paid call is then the provider's URL, not a PayAPI URL. The sequence is short. The agent calls the route with no payment. The server responds 402 and lists what it accepts: an amount in atomic units, the USDC asset contract, the payTo wallet, and the network. The agent checks those fields against the listing, signs a payment authorisation for that amount, and retries the same request with the payment header. The provider's facilitator verifies the authorisation and settles it. The provider returns the body.

There is no buyer account and no API key. The payment is the credential for that call. A later call is a new payment. Nothing is stored as credit on PayAPI's side, because PayAPI does not hold the funds. If you want a ceiling on spend, fund a wallet with a bounded USDC balance and let the agent use that wallet.

Providers list by sending one paid URL and a contact email, on the list form or through submit_listing. Price, wallet and network are read from the live 402. The listing is not settlement-verified at that moment. It becomes settlement-verified only after PayAPI has paid a route and published the receipt.

What settlement-verified means here

Settlement-verified means PayAPI Market paid one specific route from its own wallet, received a real product response, and linked the on-chain USDC receipt for that payment. The badge is that receipt. It is not a health ping and it is not a promise about the other routes on the same listing. A listing with ten routes and one paid route reads as one of ten routes settlement-verified. The listing page names the route and the transaction.

Two other labels are easy to mix up with it. "402 checked" means an unpaid request received a valid HTTP 402 for Circle USDC. Nobody paid for the product. "Listed" means the row is in the catalogue. A row imported from a public directory can show an Unclaimed provider. Those imported_unclaimed rows stay in the default catalogue so an agent can see them. They are not settlement-verified until a paid call succeeds. How we verify is the full account, with the receipt files at /verified-routes.csv and /verified-routes.json.

The homepage, this page and llms.txt all refuse to print a count that was typed in by hand. If you see a number of settlement-verified APIs, it came from that shared query on that render.

Where to go from here

Browse the grid on the marketplace, or open a category from Browse x402 APIs. Compare this catalogue with the CDP Bazaar, x402scan, x402 List and the others on x402 marketplaces compared. Hire a person's agent, or list your own, on the agent marketplace. The AI agent marketplace guide explains how that product differs from the API catalogue.

A longer essay on the same idea lives at What is an x402 marketplace. The x402 Bazaar alternatives guide is a narrative comparison. The page linked above is the table with a source on every figure.

Live counts

At this render (13 November 2026) the same catalogue query that writes llms.txt counted 1,559 settlement-verified APIs, 2,755 listed. /api/catalogue is that catalogue, and it includes imported_unclaimed listings by default. llms.txt always has the latest pair. A 402 check is a separate label and is not the settlement-verified badge.

Frequently asked questions

What is an x402 marketplace?

An x402 marketplace is a public catalogue of APIs that an agent can discover and pay for one call at a time, using HTTP 402 and USDC. PayAPI Market is one x402 marketplace. The protocol is published at https://x402.org/ and is not a catalogue. The product homepage is https://payapi.market/.

How does an agent buy an API over MCP?

The agent connects to https://payapi.market/mcp and calls search_apis, list_apis or get_api. That search is free and settles nothing. The agent then calls the provider URL from the listing. The provider replies HTTP 402, the agent pays that exact USDC amount, and the provider returns the response. PayAPI takes 0% of that payment.

How does an agent buy an API over HTTP, without MCP?

Search with GET https://payapi.market/agent/search?q= and fetch one listing with GET https://payapi.market/agent/get?id= plus the slug. Then call the provider's own route unpaid, read the 402 challenge, sign a USDC payment for that amount, and retry. There is no buyer account and no API key.

Does settlement-verified mean the whole catalogue was paid for?

No. Settlement-verified means PayAPI paid one specific route from its own wallet, got a real response, and published the on-chain receipt. Other routes on the same listing, and other listings, are not covered by that receipt. A 402 check is a separate label and is not the badge.

Where do the counts on this page come from?

They are computed from the live catalogue at render time, the same query that writes https://payapi.market/llms.txt. GET https://payapi.market/api/catalogue returns those rows and includes imported_unclaimed listings by default. The page does not keep a fixed total. If the read fails, the number is left out.

What does it cost to list an API?

Listing is free, and PayAPI takes 0% of each job. Buyers pay the provider directly in USDC. PayAPI does not hold the funds and does not take a cut of the call.

What an x402 marketplace is · Browse x402 APIs · AI agent marketplace guide · x402 marketplaces compared