---
title: x402 Protocol Specification
emoji: 💳
colorFrom: green
colorTo: gray
sdk: static
sdk_version: ""
app_file: README.md
pinned: false
license: mit
---

# x402 Protocol Specification

HTTP 402 Payment Required for AI agent micropayments.

## Overview

x402 is the production implementation of HTTP 402 (reserved since 1998) for the autonomous agent economy. It enables machine-to-machine micropayments over USDC on Solana.

## How It Works

1. Agent requests a protected resource → HTTP 402 with payment challenge
2. Agent parses challenge, submits USDC payment on Solana
3. Gateway confirms settlement (~2-3 Solana slots)
4. Protected resource is returned

Total round trip: < 3 seconds. No humans. No redirects. No API keys.

## Specification

**Status**: v0.2.0 (active)

- [Full docs](https://greensol.me/nullstate/docs/protocols/x402)
- [Source code](https://github.com/nullstate/nullstate)
- [Live gateway](https://greensol.me/nullstate)

## Implementations

| Implementation | Language | Status |
|--------------|----------|--------|
| NullState Gateway | Python | Production |
| Coinbase AgentKit | TypeScript | Beta |
| AEON Protocol | Rust | Beta |

## License

MIT — do whatever you want.