Cap'n-rs – Rust implementation of Cloudflare's Cap'n Web protocol

In plain words

Cap'n-rs is a Rust implementation of Cloudflare's Cap'n Web, a schema-free capability-based RPC protocol. It provides full wire protocol compatibility with support for multiple transports including HTTP batch, WebSocket, and WebTransport, along with promise pipelining and an intermediate language expression evaluator. The tool is designed for Rust developers building distributed systems that need schema-free RPC communication with verified compatibility against the TypeScript reference implementation.

written from the facts on this page · September 2026

From the sources

Contribute to currentspace/capn-rs development by creating an account on GitHub.

In the maker’s words, at launch

Last week Cloudflare released Cap'n Web [1], a schema-free capability-based RPC protocol. I built capn-rs this week - a Rust implementation with full wire protocol compatibility. Links: GitHub: https://github.com/currentspace/capn-rs Crates…

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