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x402 Relay

Introduction

The Problem

AI agents need to use paid APIs, but they can’t:

  • Discover which APIs exist and what they cost
  • Evaluate which APIs are trustworthy
  • Pay for API calls autonomously

The Solution: x402 Relay

x402 Relay is an open-source API catalog and payment facilitator that enables AI agents to:

  1. Search a curated directory of x402-enabled APIs
  2. Evaluate APIs using Trust Scores (protocol compliance, uptime, on-chain history)
  3. Pay via HTTP 402 Payment Required protocol using USDC on Base

How Agents Use It

{
  "mcpServers": {
    "x402-relay": {
      "command": "node",
      "args": ["/path/to/x402-relay/dist/mcp-server.js"]
    }
  }
}

Via REST API

Terminal window
# Search for AI APIs
curl https://api.x402relay.com/api/services?query=image+generation


# Get service details
curl https://api.x402relay.com/api/services/svc-neural-api-1

Via SDK (Coming Soon)

import { X402Client } from '@x402relay/sdk';


const client = new X402Client();
const services = await client.search('image generation');

Architecture

AI Agent
  │
  ├─ MCP ──► x402 Relay MCP Server
  ├─ HTTP ─► x402 Relay REST API
  └─ SDK ──► @x402relay/sdk
               │
               ▼
         ┌─────────────┐
         │  Catalog DB  │  ◄── x402scan Crawler
         │  Trust Score │  ◄── On-chain Tracer
         │  Health Check│  ◄── Prober v1/v2
         └─────────────┘

Next Steps