Skip to main content
x402 lets software pay for an HTTP request the moment it makes it, with no account, subscription, or card on file. A server answers a request with 402 Payment Required and a price; the caller signs a one-time authorization to pay exactly that amount in a stablecoin such as USDC; the server verifies and delivers. It is built for machine-to-machine and agent-to-service commerce: API monetization, pay-per-call data, agentic checkout, and content metering. This page orients you and points you to the right starting path. For the protocol mechanics and the terms used throughout these docs, see x402 Concepts and Glossary. Fireblocks gives you both halves of an x402 deployment, with private keys held in Fireblocks rather than in your application:
  • A facilitator that verifies signatures and settles payments on-chain.
  • An agent that pays for x402-protected resources from a Fireblocks vault.

​
Are you selling, buying, or both?

Your first decision is which side of an x402 payment you are on. Most teams start with one and add the other later.

​
Selling: run a facilitator

The facilitator is the service your merchant server calls to verify a payment signature and settle the transfer on-chain through your Fireblocks vault. Your server keeps serving its own traffic and returns the 402 itself; customer traffic never passes through the facilitator. Once you are running, you declare the things you sell as products and, optionally, publish them so agents can discover them.

​
Buying: run an agent

The x402 Agent gives any autonomous agent the ability to pay for 402-protected resources using a Fireblocks vault. It detects the 402, signs the payment authorization through Fireblocks, and retries the request. It ships as an MCP server (for Claude Desktop, Cursor, and other MCP clients) and a CLI.

​
Hosted or open-source facilitator?

If you are selling, you choose how the facilitator runs: These docs describe the open-source facilitator you run yourself. The hosted facilitator exposes the same payment model.

​
Your path to a first payment

If you are evaluating x402 hands-on, this is the fastest route from nothing to a settled payment on a testnet:
  1. Learn the vocabulary. Skim x402 Concepts and Glossary so the rest of the docs read clearly.
  2. Set up prerequisites. Create a Fireblocks workspace, an API user, and a vault, and get testnet USDC and gas. See Prerequisites and Testnet Funds.
  3. Run the quickstart. Wire the example merchant, facilitator, and test client into one settled payment. See x402 Quickstart.
  4. Go deeper on the side you care about: Integration for selling, or Fund and Control Agent Spending for buying.
x402 is testnet-only by default on the Fireblocks facilitator. It refuses to register mainnet assets or boot with them unless you explicitly opt in. Evaluate on a testnet first, then read Operating and Production before enabling mainnet.