The x402 project combines AI and cryptocurrency to revive an unused HTTP status code: 402 Payment Required. Unlike common codes like 200 OK or 404 Not Found, 402 has been largely ignored, waiting for a practical use case.

The x402 Foundation, launched by Coinbase and Cloudflare, aims to change this by creating an open standard for cryptocurrency payments. This standard allows AI agents to pay for resources, such as API calls, directly. The idea is simple: when a resource is requested, the server responds with a 402 status code and payment details. The AI agent (or a user via a browser) includes a signed payment in the request header. The server verifies the payment through a blockchain facilitator, processes it, and grants access to the resource.

As a .NET backend developer interested in both blockchain and AI, I wanted to explore x402 in an ASP.NET environment. Since no .NET SDK existed, I started an open-source project:

https://github.com/michielpost/x402-dotnet

Currently, the SDK enables a server to issue a 402 response with payment details. A client-side implementation is still in progress.

Coinbase is already developing version 2 of the x402 standard, showing strong potential for growth. Exciting times to see AI and Crypto come together.