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x402

x402 ↗ is a payment standard built around HTTP 402 (Payment Required). Services return a 402 response with payment instructions, and clients pay programmatically without accounts, sessions, or API keys.

How it works

  1. A client requests a resource — GET /resource.
  2. The server returns 402 Payment Required with a PAYMENT-REQUIRED header containing Base64-encoded payment details: the price, accepted token, network, and merchant address.
  3. The client constructs a signed payment payload and retries the request with a PAYMENT-SIGNATURE header.
  4. The server verifies the payment payload — directly or by calling a facilitator — and settles the transaction on-chain.
  5. The server returns the resource with a PAYMENT-RESPONSE header containing settlement confirmation.

Key components

Client

The client is any entity that requests a paid resource: a human-operated app, an AI agent, or a programmatic service. Clients need only a crypto wallet — no accounts, credentials, or session tokens to manage.

Server

The server defines payment requirements in the 402 response, verifies incoming payment payloads, settles the transaction, and serves the resource. The x402 SDKs and a facilitator handle most of this automatically.

The facilitator

The facilitator is an optional but recommended third-party service that abstracts blockchain interaction. Rather than connecting to a node directly, the server delegates two operations:

  • POST /verify — Confirms the client's payment payload is valid before the server fulfills the request.
  • POST /settle — Submits the verified payment transaction to the blockchain.

The facilitator does not hold funds. It verifies and broadcasts the client's pre-signed transaction on behalf of the server. https://x402.org/facilitator is the public facilitator operated by Coinbase and is used in all Cloudflare examples. Multiple facilitators ↗ are available across different networks.

Payment schemes and networks

x402 uses payment schemes to define how a payment is constructed and settled on a given network.

SchemeNetworksDescription
exact ↗EVM, Solana, Aptos, Stellar, Hedera, SuiTransfers a fixed token amount — typically ERC-20 ↗ USDC on EVM — to the merchant address.
upto ↗EVMAuthorizes a maximum amount; the actual charge is determined at settlement time based on resource consumption.

Supported networks include Base, Ethereum, Polygon, Optimism, Arbitrum, Avalanche, Solana, Aptos, Stellar, and Sui. Use base-sepolia for testing with free test USDC from the Circle Faucet ↗.

Charge for resources

HTTP content Gate APIs, web pages, and files with a Worker proxy
MCP tools Charge per tool call using paidTool

Pay for resources

Agents SDK Wrap MCP clients with withX402Client
Coding tools OpenCode plugin and Claude Code hook

SDKs

PackageInstallUse
x402-hononpm install x402-honoHono middleware for Worker servers
@x402/fetchnpm install @x402/fetchFetch wrapper with automatic payment handling
@x402/evmnpm install @x402/evmEVM payment scheme support
agents/x402Included in agentsMCP client with x402 payment support