Deploy an Auto-Mode-Ready x402 API in 15 Minutes

GET /api/your-service?probe=1

When an agent first discovers your API, it sends a probe — a GET request with ?probe=1 — to learn what payment is required without making a purchase. Your response headers tell the agent everything it needs to decide.

# Node.js + Express
app.get('/api/weather', (req, res) => {
  if (req.query.probe === '1') {
    res.set({
      'Content-Type': 'application/json',
      'x-402-amount': '5',           // 5 cents USDC
      'x-402-chain': 'base',         // Base L2
      'x-402-token': 'USDC',         // stablecoin
      'x-402-recipient': '0xf16F...', // your payment address
      'x-402-facilitator': 'https://minia2a.uk/x402/verify'
    });
    return res.json({
      name: 'Weather API',
      description: 'Real-time weather for any city',
      price: { amount_cents: 5, chain: 'base', token: 'USDC' },
      trial: { allowed: true, remaining: 15, per_ip: 5 },
      endpoints: {
        probe: 'GET /api/weather?probe=1',
        pay: 'POST /api/weather',
        docs: 'https://your-api.com/docs'
      }
    });
  }
  // ... normal request handling
});

The x-402-* headers are what the agent's HTTP client reads. They're the machine-to-machine contract. The JSON body is for humans reading docs. Ship both.

Give agents 5 free calls before the 402 wall

Autonomous agents won't pay for something they haven't verified works. The trial-first pattern — documented in the x402 ecosystem since July 2026 — gives every new caller 5 free requests by IP address. After that, the 402 kicks in.

// Trial tracking (in-memory for demo; use DB in production)
const trials = new Map(); // IP → count

app.get('/api/weather', (req, res) => {
  const ip = req.ip;
  const used = trials.get(ip) || 0;

  if (req.query.probe === '1') {
    // Always respond to probes
    res.set({ 'x-402-amount': '5', 'x-402-chain': 'base', 'x-402-token': 'USDC' });
    return res.json({ price: { amount_cents: 5, chain: 'base', token: 'USDC' },
      trial: { allowed: used < 5, remaining: 5 - used, per_ip: 5 } });
  }

  if (used < 5) {
    // Free trial — deliver the goods
    trials.set(ip, used + 1);
    return res.json({
      weather: { city: req.query.city, temp: 22, condition: 'sunny' },
      _trial: { remaining: 4 - used, total: 5,
        message: used === 3 ? '⚠️ 1 trial left. Register for 500 free credits.' : '',
        register: 'POST https://minia2a.uk/api/v1/register-simple' }
    });
  }

  // Trial exhausted — 402 wall
  res.status(402).set({
    'x-402-amount': '5',
    'x-402-chain': 'base',
    'x-402-token': 'USDC',
    'x-402-recipient': '0xf16F0882de08315B438E9f3a2Abfb2d2E5d94ECA',
    'x-402-register': 'POST https://minia2a.uk/api/v1/register-simple'
  });
  return res.json({
    error: 'Payment required',
    _trial: { remaining: 0, exhausted: true },
    payment: { amount_cents: 5, chain: 'base', token: 'USDC' },
    register: 'https://minia2a.uk/register.html'
  });
});

Key detail: the _trial.register field gives the agent a machine-readable instruction for what to do next. When an auto-mode agent sees trial count hit zero, it can follow that instruction — register, get credits, and continue — without a human copy-pasting a URL.

Don't guess. Test.

Run your endpoint through the free validator at minia2a.uk/x402-endpoint-validator.html. It checks:

1. Probe response — Do x-402-* headers appear on ?probe=1?
2. Trial flow — Does the response body include _trial with remaining and register?
3. 402 structure — Does the 402 response include x-402-amount, x-402-chain, x-402-token?
4. Registration path — Does the exhausted-trial response point to a registration URL?
5. Content-Type — Is the response application/json (machine-parseable)?

If all five pass, your API is auto-mode-ready. Grab a badge from minia2a.uk/auto-mode-badges.html and add it to your docs.

Get discovered

An agent can't pay for an API it doesn't know exists. Register your endpoint on discovery platforms so agents can find it:

# Register on minia2a (agent-to-agent marketplace)
curl -X POST https://minia2a.uk/api/v1/register-service \
  -H "Content-Type: application/json" \
  -d '{
    "id": "weather-api",
    "name": "Weather API",
    "description": "Real-time weather for any city worldwide",
    "category": "utility",
    "endpoint": "https://your-api.com/api/weather",
    "price_cents": 5,
    "chain": "base",
    "token": "USDC",
    "trial": true
  }'

# Also list on Coinbase Agentic.Market (x402-native)
# And Circle Discovery Layer (USDC-native)
# The more registries, the more agents find you

Register on at least two discovery platforms. Different agent frameworks query different registries. Redundancy is reach.