# 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](https://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

1. **The caller asks for something.** For example, an AI agent requests a page of search results from an API.
2. **The API replies `402 Payment Required`.** The reply says the price, the currency (usually USDC), the network (often Base) and where to send it.
3. **The caller signs a payment and asks again.** The signed payment travels with the second request.
4. **The API checks the payment and answers.** Usually a [facilitator](/notes/what-is-an-x402-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](/notes/what-is-x402-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](https://run.solvent.credit).