For Developers

Build agents, build wrappers, contribute to the ecosystem.

Last updated: 2026-04-11

Quick links

• x402 protocol spec: github.com/coinbase/x402
• MCP spec: modelcontextprotocol.io
• PayAPI Market open listings endpoint: /api/listings
• MCP SSE endpoint: https://web-production-18a32.up.railway.app/mcp/sse

SDK availability

• TypeScript: x402-fetch on npm
• Python: x402-httpx on pip
• Rust: x402-reqwest on crates.io

How to wrap an existing API for x402

The PayAPI Market team maintains an open-source x402-MCP wrapper template. It's a small Express server that:

1. Sits in front of your existing API
2. Returns HTTP 402 with payment requirements on each request
3. Verifies the payment proof (a transaction hash + signature)
4. Forwards the request to your real API
5. Returns the response

You can deploy it to Railway, Fly, Vercel, or any Node host in under 10 minutes.

Frequently asked questions

Where are the official x402 SDKs?

TypeScript: x402-fetch on npm. Python: x402-httpx on pip. Rust: x402-reqwest on crates.io. All maintained by Coinbase plus community contributors.

Is there an open spec?

Yes. The x402 spec lives at github.com/coinbase/x402 and the MCP spec at modelcontextprotocol.io. Both are open and versioned.

Can I run my own facilitator?

Yes. The wrapper template uses the Coinbase facilitator by default but you can swap in any compatible facilitator URL via env var.

Are there example agents I can fork?

The PayAPI Market team maintains an example LangChain agent and an example Claude MCP client config in the wrapper-template repo.