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What is x402?

x402 is an open HTTP 402 micropayment protocol that standardizes the 402 Payment Required response headers and payload format, enabling web resources to require clients to complete on-chain payments before returning content. It defines how sellers declare payment requirements, how buyers generate payment proofs, and the complete verification and settlement flow, allowing users and AI to complete payments seamlessly.

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Core principles of x402

  1. Open standard
  2. HTTP-native
  3. Chain/Token agnostic
  4. Minimal trust
  5. Easy to use
Currently, x402 is at an early stage. The core protocol focuses on defining the basic payment flow and data formats. On EVM chains, only USDC that conforms to EIP-3009 is supported. As use cases diversify, we need extensions to support different payment types and incentive mechanisms — this is where x402x comes in.

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What is x402x?

x402x is an extension implementation of the x402 core protocol. While adhering to the core principles of x402, x402x breaks the limitations of the original protocol through an extension mechanism, supports more token standards, and introduces a facilitator incentive mechanism, enabling broader ecosystem integration and adoption. x402x extends x402 in the following ways:
  • More payment methods: supports EIP-2612 (standard Permit), EIP-3009 (USDC transferWithAuthorization), and Permit2 (Uniswap universal permit)
  • Flexible incentive mechanism: facilitator fee distribution allows payment service providers (e.g., wallets, browser extensions) to participate in the ecosystem and be incentivized
  • EIP-7702 integration: in x402x, the seller’s wallet integrates the EIP-7702 approach; buyer funds are only authorized to the seller via signature, requiring no trust in third parties, while enabling richer features via the seller wallet’s contract code
X402 Architecture

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Next steps

Quick Start

Get the end-to-end flow running in 5 minutes

Core Concepts

Understand the protocol and minimal-trust design

Seller Guide

How servers declare payment requirements and settle

Buyer Guide

How clients automatically complete payments