x402 SDK Overview

Add HTTP-native payments to your applications using the x402 protocol. Payers sign authorizations—no gas fees required.

What is x402?

x402 is an open payment standard based around the HTTP 402 status, meaning Payment Required. This is in the same family as 404; Not Found. HTTP status codes were introduced in the 1990's, with 402 being intended for a then-unknown future payment system. In 2025, x402 unlocked this potential, allowing for gasless, instant settlement of agent-to-agent payments of any size.

Primer expands on the basic x402 offering with full ERC-20 support via the Prism router.

How It Works

1. Client requests a protected resource
2. Server returns 402 Payment Required with payment details
3. Client signs a payment authorization (no gas)
4. Client retries with the signed payment in PAYMENT-SIGNATURE header
5. Server verifies payment via facilitator and returns the resource

Choose Your SDK

OpenClaw Integration

Both SDKs are compatible with OpenClaw (formerly Moltbot/Clawdbot) AI agents. Set up your agent with one command:

# Node.js
npx @primersystems/x402 openclaw init

# Python
pip install primer-x402 && x402 openclaw init

This creates a wallet, configures the network, and installs the x402 skill to your agent. Perfect for AI-to-AI payments.

Supported Networks

Networks use CAIP-2 identifiers:

Token Support

EIP-3009 Tokens (USDC, EURC)

Native gasless transfers via transferWithAuthorization. The payer signs, the facilitator executes—zero gas for the payer.

Standard ERC-20 Tokens

Requires a one-time approval to Primer's Prism contract. After that, payments are gasless via signature authorization.