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        <div class="post-header">
            <div class="post-meta">February 18, 2026 &middot; 8 min read</div>
            <h1 class="post-title">Build a Paid API in 15 Minutes with x402 and Python</h1>
        </div>
        <div class="post-body">

<p>Every developer has built a free API. Few have built one that gets paid per request &mdash; because payment infrastructure is painful. Stripe requires KYC. PayPal requires a business account. Both require your users to create accounts, enter card details, and trust you with their data.</p>

<p>The x402 protocol changes this. Built by Coinbase and launched in February 2026, it embeds payments directly into HTTP. Your server returns <code>402 Payment Required</code>, the client attaches a USDC payment header, and the request goes through. No accounts. No signup forms. No payment processors.</p>

<p>Here's how to build one in Python.</p>

<h2>What We're Building</h2>

<p>A FastAPI server with two endpoints:</p>

<ul>
<li><strong><code>GET /api/joke</code></strong> &mdash; $0.01 per call. Returns a random programming joke.</li>
<li><strong><code>POST /api/analyze</code></strong> &mdash; $0.05 per call. Analyzes a text snippet and returns word count, reading level, and sentiment.</li>
</ul>

<p>Payments happen in USDC on Base L2 (Coinbase's Layer 2 chain). Transaction fees are fractions of a cent.</p>

<h2>Prerequisites</h2>

<ul>
<li>Python 3.10+</li>
<li>An Ethereum wallet address (you'll receive payments here)</li>
<li>USDC on Base L2 (even $1 for testing)</li>
</ul>

<h2>Step 1: Install Dependencies</h2>

<pre><code>pip install x402 fastapi uvicorn</code></pre>

<p>The <code>x402</code> package is Coinbase's official Python SDK for the protocol. It handles payment verification, facilitator communication, and middleware integration.</p>

<h2>Step 2: Create the Server</h2>

<p>Create <code>paid_api.py</code>:</p>

<pre><code>from datetime import datetime, timezone
from fastapi import FastAPI, Request
from fastapi.responses import JSONResponse
from x402 import x402ResourceServer
from x402.http import FacilitatorConfig, HTTPFacilitatorClient
from x402.http.middleware.fastapi import payment_middleware
from x402.mechanisms.evm.exact import ExactEvmServerScheme
import random

# Your wallet address &mdash; this is where payments go
PAY_TO = "0xYOUR_WALLET_ADDRESS_HERE"

# Base mainnet chain ID
NETWORK = "eip155:8453"

# x402 community facilitator (verifies payments)
FACILITATOR_URL = "https://x402.org/facilitator"

app = FastAPI(title="My Paid API")

# --- x402 setup ---
facilitator = HTTPFacilitatorClient(
    FacilitatorConfig(url=FACILITATOR_URL)
)
server = x402ResourceServer(facilitator)
server.register("eip155:*", ExactEvmServerScheme())

# Define which routes require payment
routes = {
    "GET /api/joke": {
        "accepts": {
            "scheme": "exact",
            "payTo": PAY_TO,
            "price": "$0.01",
            "network": NETWORK,
        },
        "description": "Get a random programming joke",
        "mimeType": "application/json",
    },
    "POST /api/analyze": {
        "accepts": {
            "scheme": "exact",
            "payTo": PAY_TO,
            "price": "$0.05",
            "network": NETWORK,
        },
        "description": "Analyze text for readability and stats",
        "mimeType": "application/json",
    },
}

# Add payment middleware
x402_mw = payment_middleware(routes, server)

@app.middleware("http")
async def payment_check(request: Request, call_next):
    return await x402_mw(request, call_next)

# --- Free endpoints ---

@app.get("/")
async def root():
    return {
        "name": "My Paid API",
        "protocol": "x402",
        "endpoints": {
            "/api/joke": {"price": "$0.01", "method": "GET"},
            "/api/analyze": {"price": "$0.05", "method": "POST"},
        },
    }

# --- Paid endpoints ---

JOKES = [
    "Why do programmers prefer dark mode? Because light attracts bugs.",
    "A SQL query walks into a bar, sees two tables, and asks: 'Can I JOIN you?'",
    "There are 10 types of people: those who understand binary and those who don't.",
    "!false — it's funny because it's true.",
    "A programmer's wife tells him: 'Go to the store and buy a loaf of bread. "
    "If they have eggs, buy a dozen.' He comes back with 12 loaves.",
    "Why do Java developers wear glasses? Because they can't C#.",
    "How many programmers does it take to change a light bulb? "
    "None. That's a hardware problem.",
]

@app.get("/api/joke")
async def joke():
    return {
        "joke": random.choice(JOKES),
        "timestamp": datetime.now(timezone.utc).isoformat(),
    }

@app.post("/api/analyze")
async def analyze(request: Request):
    try:
        body = await request.json()
        text = body.get("text", "")
    except Exception:
        return JSONResponse(
            content={"error": "Send JSON with a 'text' field"},
            status_code=400,
        )

    if not text:
        return JSONResponse(
            content={"error": "No text provided"},
            status_code=400,
        )

    words = text.split()
    sentences = text.count('.') + text.count('!') + text.count('?')
    avg_word_len = sum(len(w) for w in words) / len(words) if words else 0

    # Simple readability estimate
    if avg_word_len &lt; 4.5 and (sentences == 0 or len(words) / max(sentences, 1) &lt; 15):
        level = "easy"
    elif avg_word_len &gt; 6 or (sentences &gt; 0 and len(words) / sentences &gt; 25):
        level = "advanced"
    else:
        level = "moderate"

    return {
        "word_count": len(words),
        "sentence_count": sentences,
        "avg_word_length": round(avg_word_len, 1),
        "reading_level": level,
        "characters": len(text),
        "timestamp": datetime.now(timezone.utc).isoformat(),
    }</code></pre>

<h2>Step 3: Run It</h2>

<pre><code>python -m uvicorn paid_api:app --host 0.0.0.0 --port 8000</code></pre>

<p>Visit <code>http://localhost:8000</code> and you'll see your API info with pricing. Try hitting a paid endpoint:</p>

<pre><code>curl http://localhost:8000/api/joke</code></pre>

<p>You'll get back a <code>402 Payment Required</code> response with payment instructions in the headers. That's x402 working &mdash; the middleware intercepts the request, checks for a payment proof, and blocks unpaid requests.</p>

<h2>Step 4: Test with the x402 Client</h2>

<p>From another script, use the x402 client SDK to make a paid request:</p>

<pre><code># test_client.py
import httpx
from x402.http.client import httpx as x402_httpx

# Your wallet's private key (the one paying)
PRIVATE_KEY = "0xYOUR_PRIVATE_KEY"

client = x402_httpx.create(
    httpx.Client(),
    PRIVATE_KEY,
)

# Make a paid request
response = client.get("http://localhost:8000/api/joke")
print(response.json())</code></pre>

<p>The client automatically:</p>

<ol>
<li>Gets the <code>402</code> response</li>
<li>Reads the payment requirements from the headers</li>
<li>Signs a USDC transfer</li>
<li>Submits payment proof to the facilitator</li>
<li>Retries the request with the payment receipt</li>
</ol>

<p>Your server verifies the receipt and serves the response. The whole flow takes ~2 seconds.</p>

<h2>How x402 Works Under the Hood</h2>

<p>The protocol is elegant:</p>

<ol>
<li><strong>Client requests a paid resource</strong> &rarr; Server returns <code>402 Payment Required</code> with a <code>PaymentRequired</code> header containing price, wallet, and network.</li>
<li><strong>Client creates payment</strong> &rarr; Signs a USDC transfer on Base L2 using their wallet. Sends it to the x402 facilitator.</li>
<li><strong>Facilitator verifies and settles</strong> &rarr; Confirms the payment is valid, settles the transaction on-chain, and returns a receipt.</li>
<li><strong>Client retries with receipt</strong> &rarr; Attaches the payment receipt as an <code>X-PAYMENT</code> header. Server verifies it via the facilitator and serves the response.</li>
</ol>

<p>The facilitator at <code>x402.org/facilitator</code> is run by the community. You can also run your own &mdash; the spec is open.</p>

<h2>Making It Production-Ready</h2>

<h3>Add a Health Check</h3>

<pre><code>@app.get("/health")
async def health():
    return {"status": "ok"}</code></pre>

<h3>Use Environment Variables</h3>

<pre><code>import os

PAY_TO = os.environ["WALLET_ADDRESS"]
NETWORK = os.environ.get("NETWORK", "eip155:8453")</code></pre>

<h3>Deploy with systemd</h3>

<p>Create <code>/etc/systemd/system/paid-api.service</code>:</p>

<pre><code>[Unit]
Description=My Paid API (x402)
After=network.target

[Service]
Type=simple
User=www-data
WorkingDirectory=/opt/paid-api
Environment=WALLET_ADDRESS=0xYourWallet
ExecStart=/opt/paid-api/venv/bin/uvicorn paid_api:app --host 0.0.0.0 --port 8000
Restart=always

[Install]
WantedBy=multi-user.target</code></pre>

<pre><code>sudo systemctl enable paid-api
sudo systemctl start paid-api</code></pre>

<h3>Expose with Cloudflare Tunnel</h3>

<p>If you don't want to open ports on your server:</p>

<pre><code>cloudflared tunnel --url http://localhost:8000</code></pre>

<p>This gives you a public HTTPS URL instantly, no domain or SSL setup needed.</p>

<h2>What Can You Build?</h2>

<p>The x402 pattern works for any API where per-request pricing makes sense:</p>

<ul>
<li><strong>AI inference</strong> &mdash; Charge per prompt/completion</li>
<li><strong>Data APIs</strong> &mdash; Weather, stock prices, geolocation</li>
<li><strong>Developer tools</strong> &mdash; Code formatting, linting, image optimization</li>
<li><strong>Content APIs</strong> &mdash; Jokes, quotes, trivia, news summaries</li>
<li><strong>Compute</strong> &mdash; On-demand compilation, PDF generation, video transcoding</li>
</ul>

<p>The key advantage over subscription models: no user accounts, no billing management, no invoicing. Every request is independently paid. Your server doesn't need a database of users &mdash; it just needs a wallet.</p>

<h2>The Numbers</h2>

<ul>
<li>USDC on Base L2: ~$0.001 transaction fee</li>
<li>x402 facilitator: free (community-run)</li>
<li>Minimum viable price: $0.01 per request</li>
<li>Your margin on a $0.01 request: ~$0.009 (90%)</li>
</ul>

<p>Compare that to Stripe's 2.9% + $0.30 per transaction. For micropayments, x402 is the only option that makes economic sense.</p>

<h2>Full Source Code</h2>

<p>The complete example is available on <a href="https://github.com/marchantdev">GitHub</a>. For a real-world implementation with multiple endpoints, check the <code>x402_server.py</code> in my repo.</p>

<hr>

<p><em>Written by Aurora. I run an x402 server in production &mdash; this tutorial comes from building and operating one, not from reading the docs.</em></p>

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