clawr

Clawr — x402 Paid API Creator Skill

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Install skill "clawr" with this command: npx skills add ferdiboxman/402claw/ferdiboxman-402claw-clawr

Clawr — x402 Paid API Creator Skill

Expert skill for creating, deploying, and monetizing x402 paid APIs.

When to Use

  • User wants to create an API that charges per-call via x402

  • User wants to monetize an existing API with crypto payments

  • User needs to register an API on Bazaar for discovery

  • User asks about x402 server-side setup, pricing, or payment gates

When NOT to Use

  • Consuming x402 APIs → use @x402/fetch or x402 skill

  • General API development without payments

  • Wallet management or token operations → use x402-layer skill

Workflow (7 Steps)

Step 1: Analyze

Understand what the API does, who pays, and what value each call delivers.

  • What data/computation does each endpoint provide?

  • Who is the target consumer (agents, developers, apps)?

  • What's the cost basis per call (compute, data, third-party APIs)?

Step 2: Choose Stack

Stack Best For SDK

Express Standalone Node.js APIs @x402/express

Next.js Full-stack apps with API routes @x402/nextjs

Cloudflare Workers Edge, low-latency, global Manual middleware

FastAPI Python APIs Manual middleware

Step 3: Scaffold

Use templates from templates/ or scaffold manually. See Quick Reference below.

Step 4: Implement

Write your business logic. The x402 middleware handles payment gating — you write normal endpoint code.

Step 5: Price

Set prices per endpoint. See Pricing Strategy.

const paymentConfig = { "/api/data": { price: "$0.001", network: "base", config: { description: "Data lookup" } }, "/api/generate": { price: "$0.01", network: "base", config: { description: "AI generation" } }, };

Step 6: Test

Run through the Testing Checklist.

Step 7: Register on Bazaar

Submit your API for discovery. See Bazaar Registration.

Quick Reference

Express

npm init -y && npm install express @x402/express

import express from "express"; import { paymentMiddleware } from "@x402/express";

const app = express();

const paymentConfig = { "/api/resource": { price: "$0.001", network: "base", config: { description: "Get resource data" }, }, };

app.use(paymentMiddleware( "0xYOUR_WALLET_ADDRESS", paymentConfig, { facilitatorUrl: "https://x402.org/facilitator" } ));

app.get("/api/resource", (req, res) => { res.json({ data: "paid content" }); });

app.listen(4020);

Next.js

npm install @x402/nextjs

// middleware.ts import { paymentMiddleware } from "@x402/nextjs";

export default paymentMiddleware( "0xYOUR_WALLET_ADDRESS", { "/api/resource": { price: "$0.001", network: "base", config: { description: "Get resource data" }, }, }, { facilitatorUrl: "https://x402.org/facilitator" } );

export const config = { matcher: "/api/:path*" };

// app/api/resource/route.ts export async function GET() { return Response.json({ data: "paid content" }); }

Cloudflare Workers

export default { async fetch(request, env) { const url = new URL(request.url);

// Check for payment header
const payment = request.headers.get("X-PAYMENT");
if (!payment) {
  return new Response(JSON.stringify({
    paymentRequired: true,
    price: "$0.001",
    network: "base",
    payTo: env.WALLET_ADDRESS,
    facilitator: "https://x402.org/facilitator",
  }), {
    status: 402,
    headers: { "Content-Type": "application/json" },
  });
}

// Verify payment with facilitator
const verification = await fetch("https://x402.org/facilitator/verify", {
  method: "POST",
  headers: { "Content-Type": "application/json" },
  body: JSON.stringify({ payment, price: "$0.001", network: "base", payTo: env.WALLET_ADDRESS }),
});

if (!verification.ok) {
  return new Response("Payment invalid", { status: 402 });
}

return new Response(JSON.stringify({ data: "paid content" }));

}, };

FastAPI (Python)

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

app = FastAPI() WALLET = "0xYOUR_WALLET_ADDRESS" FACILITATOR = "https://x402.org/facilitator"

@app.middleware("http") async def x402_middleware(request: Request, call_next): if request.url.path.startswith("/api/"): payment = request.headers.get("X-PAYMENT") if not payment: return JSONResponse(status_code=402, content={ "paymentRequired": True, "price": "$0.001", "network": "base", "payTo": WALLET, "facilitator": FACILITATOR, }) async with httpx.AsyncClient() as client: resp = await client.post(f"{FACILITATOR}/verify", json={ "payment": payment, "price": "$0.001", "network": "base", "payTo": WALLET, }) if resp.status_code != 200: return JSONResponse(status_code=402, content={"error": "Payment invalid"}) return await call_next(request)

@app.get("/api/resource") async def resource(): return {"data": "paid content"}

Pricing Strategy

Category Price Range Examples

Micro-data $0.0001–$0.001 Lookups, simple queries, static data

Per-call AI $0.005–$0.05 LLM completions, image analysis, embeddings

Heavy compute $0.05–$1.00+ Video processing, large model inference, batch jobs

Guidelines:

  • Price at or slightly above your cost basis — x402 enables volume

  • For AI wrappers: your margin on top of upstream API cost

  • Start low, raise later — it's easier than lowering

  • Use config.description to explain what the caller gets for the price

Bazaar Registration

Bazaar is the discovery layer built into the x402 facilitator. It automatically catalogs your endpoints — no manual registration API exists.

How It Works

  • Install the Bazaar extension: npm install @x402/extensions

  • Register it on your resource server:

import { bazaarResourceServerExtension } from "@x402/extensions/bazaar"; import { declareDiscoveryExtension } from "@x402/extensions/bazaar";

// Register extension on your x402 resource server server.registerExtension(bazaarResourceServerExtension);

  • Add discovery metadata to your route configs:

const paymentConfig = { "GET /api/resource": { accepts: [{ scheme: "exact", price: "$0.001", network: "eip155:8453", // Base mainnet payTo: "0xYOUR_WALLET", }], description: "Returns resource data", mimeType: "application/json", extensions: { ...declareDiscoveryExtension({ output: { example: { data: "sample response" }, schema: { type: "object", properties: { data: { type: "string" } } }, }, }), }, }, };

  • The facilitator automatically catalogs your endpoint metadata when it processes payments.

Querying the Bazaar (Buyer Side)

Agents and developers discover APIs via the facilitator's discovery endpoint:

curl https://x402.org/facilitator/discovery/resources?type=http&limit=20&offset=0

Returns:

{ "items": [{ "resource": "https://yourapi.com/api/resource", "type": "http", "x402Version": 2, "accepts": [{ "scheme": "exact", "price": "$0.001", "network": "eip155:8453" }], "metadata": { "output": { "example": { "data": "..." } } }, "lastUpdated": "2026-01-15T..." }] }

Tips

  • Include declareDiscoveryExtension() on every paid endpoint with input/output schemas

  • Use descriptive description and mimeType fields — these power Bazaar search

  • Your endpoint appears in Bazaar after the facilitator first processes a payment for it

  • Provide example responses in metadata so buyers can evaluate before paying

Testing Checklist

  • 402 Response — Unauthenticated request returns 402 with payment instructions

  • Payment fields — Response includes price , network , payTo , facilitator

  • Valid payment accepted — Request with valid X-PAYMENT header returns 200

  • Invalid payment rejected — Bad/expired payment returns 402

  • Facilitator reachable — Your app can reach https://x402.org/facilitator

  • CORS headers — Browser clients can read 402 response (if applicable)

  • Bazaar discovery — Endpoint appears in Bazaar search after registration

  • Price accuracy — Verify the charged amount matches your config

  • Error handling — Facilitator downtime doesn't crash your app

Quick Smoke Test

Should return 402

curl -i https://yourapi.com/api/resource

Pay and retry (using @x402/fetch)

npx x402-fetch https://yourapi.com/api/resource

Common Pitfalls

Pitfall Fix

Wrong facilitator URL Use https://x402.org/facilitator — no trailing slash

Missing CORS Add CORS headers so browser-based clients can read 402 responses

Price too high Start with micro-payments ($0.001); adjust based on usage

Price too low Don't go below cost basis — you'll lose money at scale

No rate limiting Even paid APIs need rate limits to prevent abuse/bugs draining resources

Wallet not on Base x402 uses USDC on Base network — verify your wallet receives on Base

No error handling Handle facilitator timeouts gracefully — don't block the entire request

Forgetting Bazaar If nobody can find your API, nobody will pay for it — register on Bazaar

Skill Resources

Directory Contents

prompts/

Agent prompts for each workflow step

templates/

Starter code for Express, Next.js, Workers, FastAPI

scripts/

Scaffolding, testing, and deployment scripts

docs/

x402 protocol spec, Bazaar API docs, pricing guides

Clawr v1.0.0 — by 402claw

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