r402-mcp

Model Context Protocol (MCP) transport for the x402 payment protocol.

Status

Placeholder. This crate reserves the r402-mcp name and documents the design intent for an MCP transport. Concrete implementations (server and client modules) will land in a subsequent release. Track progress in the repository's issue tracker.

Design Intent

The MCP transport will layer x402 on top of Model Context Protocol tool calls:

• Server side: wrap tool invocations with a paygate that emits a PaymentRequired payload in the tool's _meta["x402/payment"] block, producing an isError: true response until a valid payment is presented.
• Client side: a middleware that automatically signs and replays tool calls upon receiving a PaymentRequired response.

The wire-level types are shared with r402-core; only the transport framing differs from the HTTP variant.

License

Licensed under either of MIT or Apache-2.0, at your option.