x402 Protocol

Last reviewed: 2026-04-28

by Coinbase — open standard · github.com/coinbase/x402

Payment Rail Open Source Official

Best for: Machine-to-machine pay-per-request payments; micropayments for API access without auth tokens

Not ideal for: User-to-agent payments; fiat currency; high-value single transactions

Key Signals

Payment Mechanism

HTTP 402 native

Currency

USDC

Client Requirement

Any HTTP client

Pricing

Free (open protocol)

Features

🔁

HTTP 402-Based Payment Protocol

Revives the long-dormant HTTP 402 "Payment Required" status code. Servers respond with 402 and payment details; clients attach payment proof and retry. No OAuth dance, no API keys — payment IS the authentication.

🔑

No Auth Tokens Needed

Eliminates credential management entirely for M2M scenarios. The cryptographic payment proof doubles as proof of authorization. AI agents can access paid APIs without pre-provisioned credentials or subscription accounts.

💵

USDC Per-Request Settlement

Each API request can carry a USDC micropayment settled on Base. Enables granular pay-per-call pricing that would be impractical with traditional invoicing. Fractions of a cent per call are economically viable.

🌐

Any Language / Framework

Works with any HTTP client in any language. Reference implementations available in JavaScript/TypeScript and Python. Middleware packages available for Express, Next.js, and FastAPI to add 402 support in minutes.

Ratings

Protocol Simplicity

4.8

Agent Compatibility

4.7

Ecosystem Maturity

3.2

Ease of Integration

4.3

Ratings based on documentation review, GitHub activity, and public developer reports. Not independently verified in production.

Integration

# 1. curl example — server returns 402, client retries with payment header
curl -i https://api.example.com/data
# HTTP/1.1 402 Payment Required
# x-payment-required: {"scheme":"exact","network":"base","maxAmountRequired":"1000","resource":"https://api.example.com/data","description":"1 USDC per call","mimeType":"application/json","payTo":"0xSERVER_ADDRESS","maxTimeoutSeconds":60,"asset":"0x833589fCD6eDb6E08f4c7C32D4f71b54bdA02913"}

curl -H "x-payment: SIGNED_PAYMENT_PAYLOAD" https://api.example.com/data

# 2. JS fetch with x402 client middleware
npm install x402-fetch

import { wrapFetch } from 'x402-fetch';
import { createWalletClient } from 'viem';

const wallet = createWalletClient({ ... });
const fetchWithPayment = wrapFetch(fetch, wallet);

// Automatically handles 402 → sign payment → retry
const res = await fetchWithPayment('https://api.example.com/data');
const data = await res.json();
        

Alternatives

Stripe Agent Toolkit

Traditional fiat rails with full Stripe ecosystem — better for user-facing checkout flows

→

Skyfire

Hosted agent payment service — managed alternative if you don't want to run your own x402 infrastructure

→

Payman AI

Human-in-the-loop payment approval — better when humans need to authorize agent spending

→