x402 is an internet-native payments protocol that enables agents to send and receive payments for services. This helps developers build autonomous agents and agentic applications directly on SKALE. This guide covers the essential concepts for building agents that interact with x402 payments.
What is x402?
x402 is a payment protocol that extends HTTP with native payment capabilities using the 402 Payment Required status code. It enables:
- Paywalled Resources: Protect APIs and services behind payments
- Autonomous Payments: Agents can automatically pay for and access resources
- ERC-3009 Compatibility: Uses
TransferWithAuthorization for gasless payments
- Multi-Token Support: Accept payments in various ERC-20 tokens
Core Components
1. Facilitator
A facilitator processes x402 payments by exposing endpoints that verify and settle payment authorizations:
/verify - Validates payment signatures without executing onchain/settle - Executes the onchain payment settlement
Facilitators generally support a 3rd endpoint — /supported — which allows agents to discover resources.
2. Payment Middleware
Middleware that protects HTTP endpoints by enforcing the x402 payment handshake:
- Returns
402 Payment Required when payment is missing
- Forwards payment to facilitator for verification
- Allows request to proceed after successful settlement
The middleware is implemented at the seller/merchant level and is able to be fully stateless. This is done through the use of a 3rd party facilitator who handles the above verification and settlement on your behalf.
3. Payment Client
Client libraries that handle the x402 payment flow automatically:
- Detect
402 Payment Required responses
- Create and sign payment authorizations
- Retry requests with proper payment headers
Learn More: Make Payments
Quick Start: Build a Payment-Enabled Agent
Here’s a minimal example of an agent that can access paywalled resources:
import { x402Client, x402HTTPClient } from "@x402/core/client";
import { ExactEvmScheme } from "@x402/evm";
import { privateKeyToAccount } from "viem/accounts";
// Setup wallet
const account = privateKeyToAccount(process.env.PRIVATE_KEY as `0x${string}`);
// Create x402 client
const evmScheme = new ExactEvmScheme(account);
const coreClient = new x402Client().register("eip155:*", evmScheme);
const httpClient = new x402HTTPClient(coreClient);
// Access paywalled resource
async function accessResource(url: string) {
try {
const response = await fetch(url);
if (response.status === 402) {
// Get payment requirements
const responseBody = await response.json();
const paymentRequired = httpClient.getPaymentRequiredResponse(
(name) => response.headers.get(name),
responseBody
);
// Create payment payload
const paymentPayload = await httpClient.createPaymentPayload(paymentRequired);
const paymentHeaders = httpClient.encodePaymentSignatureHeader(paymentPayload);
// Retry with payment
const paidResponse = await fetch(url, {
headers: { ...paymentHeaders }
});
if (!paidResponse.ok) {
throw new Error(`Request failed: ${paidResponse.status}`);
}
return paidResponse.json();
}
if (!response.ok) {
throw new Error(`Request failed: ${response.status}`);
}
return response.json();
} catch (error) {
console.error("Error accessing resource:", error);
throw error;
}
}
Use Cases
Autonomous Service Access
Build agents that pay for API calls, data feeds, or AI services:
// Agent pays for weather data automatically
const weatherData = await agent.accessResource("https://api.example.com/weather");
Monetize Agent Services
Create services where agents pay to access your AI models or data:
// Protect your AI endpoint with x402
app.get("/ai/analyze", paymentMiddleware, async (c) => {
const result = await model.analyze(c.req.query);
return c.json(result);
});
Multi-Agent Economies
Enable agents to pay each other for services in a decentralized economy:
// Agent A requests work from Agent B, pays automatically
const result = await agentA.requestWork(agentB.endpoint, taskData);
Payment Tokens on SKALE
SKALE Base Sepolia Testnet supports various tokens for x402 payments:
| Token | Address | Decimals |
|---|
| Axios USD | 0x61a26022927096f444994dA1e53F0FD9487EAfcf | 6 |
| Bridged USDC | 0x2e08028E3C4c2356572E096d8EF835cD5C6030bD | 6 |
Resources
