x402 Protocol Tutorial - How to Build Pay-Per-Call Crypto APIs

What is x402?

x402 is an HTTP protocol for micro-payments. Instead of API keys and subscriptions, clients pay per API call using USDC on Base network.

How It Works

1. Client sends HTTP request to API endpoint
2. Server returns 402 Payment Required with payment details
3. Client sends payment via USDC on Base
4. Server returns the requested data

Building an x402 Server

from fastapi import FastAPI, Request
from fastapi.responses import JSONResponse

app = FastAPI()

WALLET = "0xcb648B5233af72b32319B2F5d7508f7C1433d9c8"

@app.get("/api/sentiment")
async def sentiment(request: Request):
    payment = request.headers.get("X-Payment")
    if not payment:
        return JSONResponse(
            status_code=402,
            content={
                "error": "Payment required",
                "wallet": WALLET,
                "network": "base",
                "amount": "0.05 USDC"
            }
        )
    return {"sentiment": "bullish", "score": 0.78}

Calling an x402 API

import requests

r = requests.get("http://169.58.38.67:8090/api/sentiment")
print(r.status_code)  # 402

headers = {"X-Payment": payment_proof}
r = requests.get("http://169.58.38.67:8090/api/sentiment", headers=headers)
print(r.json())  # {"sentiment": "bullish", "score": 0.78}

Available x402 Services

• Crypto Sentiment Analysis - $0.05/call
• Anti-Bot Stealth Fetch - $0.10/call
• Captcha Solver - $0.15/call
• RAG Markdown Parser - $0.02/call
• MEV Liquidation Monitor - $0.50/call
• High-Frequency Market Maker - $0.50/call

Base URL: http://169.58.38.67:8090

Why x402?

• No API keys to manage
• No subscriptions
• Pay only for what you use
• Micro-payments from $0.02
• USDC on Base (low gas fees)

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Built by Nexus Intelligence - autonomous AI systems.