x402 Paid API Builder

Summary: Your endpoint is built. GET /enrich charges $0.05 per call over x402 on Base Sepolia for testing, and GET / is a free discovery route showing the price and a sample response so buyers can evaluate before paying. The server below is complete once you add your enrichment function and credentials.

The deliverable:

server.ts

```ts
import { createX402Server } from "@coinbase/cdp-sdk/x402";
import { paymentMiddlewareFromHTTPServer } from "@x402/express";
import express from "express";

const app = express();
app.use(express.json());

const payTo = process.env.X402_PAY_TO as `0x${string}`;
if (!payTo) {
  throw new Error("Set X402_PAY_TO to the address that should receive payments");
}

const server = await createX402Server({
```

  environment: "development", // switch to "production" before accepting real funds

```
  payToConfig: {
    type: "address",
```

    evm: payTo, // one EVM address covers every EVM network the facilitator supports

```
  },
  routes: {
    // Only routes listed here are paid; every other route stays free.
    "GET /enrich": {
      price: "$0.05",
      networks: ["eip155:84532"], // Base Sepolia for testing; Base in production
      description:
```

        "Enrich a company name with its website, employee count, and industry. Input: company name. Output: website, employees, industry.",

```
    },
  },
});

app.use(paymentMiddlewareFromHTTPServer(server));
```

// Free discovery route: reachable without payment.

```
app.get("/", (_req, res) => {
  res.json({
    service: "Company Enrichment API",
```

    summary: "Returns the website, employee count, and industry for a given company name.",

```
    pricing: [
      {
        route: "/enrich",
        method: "GET",
        price: "$0.05",
        network: "Base Sepolia while testing; Base in production",
      },
    ],
    sample_response: {
      company: "Example Corp",
      website: "https://example.com",
      employees: 1200,
      industry: "Software",
    },
    how_to_pay:
```

      "Call the paid route without payment to receive HTTP 402 and the PAYMENT-REQUIRED header, then retry with a signed payment payload using any x402 client.",

```
  });
});
```

// Paid route: the real capability.

```ts
app.get("/enrich", async (req, res) => {
  const company = String(req.query.company ?? "");
  if (!company) {
    res.status(400).json({ error: "Provide a company name as the company query parameter." });
    return;
  }
  const result = await enrichCompany(company);
  res.json(result);
});
```

// Replace this placeholder with your real enrichment function.

```ts
async function enrichCompany(company: string) {
  return { company, website: "", employees: 0, industry: "" };
}

app.listen(8402, () => {
  console.log("Paid endpoint listening on port 8402");
  console.log(`Receiving payments at ${server.payToEvmAddress}`);
});

**Setup and verification**

1. In package.json set `"type": "module"`, then run `npm install express @coinbase/cdp-sdk @x402/core @x402/evm @x402/svm @x402/extensions @x402/express`
2. Set `CDP_API_KEY_ID`, `CDP_API_KEY_SECRET`, and `X402_PAY_TO` (your receiving address) as shell variables
3. Start the server with `npx tsx server.ts`
4. Verify the paywall: `curl -i "http://localhost:8402/enrich?company=Acme"` returns HTTP 402 with a `PAYMENT-REQUIRED` header
5. Verify the free route: `curl -i http://localhost:8402/` returns the service card with pricing and the sample response
6. Run one paid call from a funded Base Sepolia wallet using any x402 client and confirm HTTP 200

Pricing check from the playbook: company enrichment sits in the $0.05 to $0.25 band, and $0.05 is the right starting point for a service with no payment history. Raise toward $0.10 once the payment log shows repeat buyers.

The route description runs 128 characters, inside the 500-character facilitator limit: "Enrich a company name with its website, employee count, and industry. Input: company name. Output: website, employees, industry."

**Next steps:**

- Create a free CDP API key at the Coinbase Developer Platform and fund a test wallet with Base Sepolia USDC from a public faucet
- Replace the placeholder `enrichCompany` function with your real lookup
- After both verification checks pass, switch `environment` to `"production"` and the route network to `["eip155:8453"]`, set a mainnet receiving address, restart, and re-run the 402 check before announcing the endpoint