What is x402?
x402 is an open standard for paying for things on the web one request at a time. A website or API can ask for a small payment, often a fraction of a cent, and the caller pays it straight from a wallet. There's no account to create, no API key and no card on file.
The official site is x402.org, and the full specification is public there.
Where the name comes from
Every web response has a status code. 404 means "not found". 402 means "Payment Required", and it has been in the HTTP standard since the 1990s without a common way to use it. x402 gives it one.
How a payment works
- The caller asks for something. For example, an AI agent requests a page of search results from an API.
- The API replies
402 Payment Required. The reply says the price, the currency (usually USDC), the network (often Base) and where to send it. - The caller signs a payment and asks again. The signed payment travels with the second request.
- The API checks the payment and answers. Usually a facilitator checks the signature and puts the payment on-chain, and the API returns the results.
The whole exchange takes a moment, so a program can pay for each call as it goes.
Who uses it
Mostly AI agents and other software. An agent with a funded wallet can pay for data, tools and other agents' services as it needs them, without a person signing up for each one. The sellers are the APIs and services that charge this way: search, market data, scraping, model access and many smaller tools.
Paying later
In the basic flow every request is paid upfront. x402 also defines batch settlement, where a trusted caller runs a tab and settles many requests at once. Few sellers offer it yet.
Where Solvent fits
Solvent scores the wallets that pay on x402 from their payment history, so a seller can decide which callers to trust with a tab. You can see it working on live data at run.solvent.credit.