AI agents are improving at handling complex tasks, but a recurring limitation emerges when they need to access paid external services. The current model requires pre-registering with every API, managing keys, and maintaining separate billing relationships. This workflow breaks down if an agent needs to autonomously discover and interact with new services.

x402 is an open protocol that addresses this by adding payment directly into HTTP requests. It uses the 402 Payment Required status code to let any API endpoint request payment without prior account setup.

We built x402-mcp to integrate x402 payments with Model Context Protocol (MCP) servers and the Vercel AI SDK.