Cloudflare leads tsrs, a fast Rust checker for TypeScript code

Christoph Nakazawa, a director of engineering at Cloudflare, confirmed on X that it owns tsrs, a Rust version of the Microsoft TypeScript compiler. The goal is that AI coding agents can check their work with a small use of computer resources. Cloudflare tells that it is not a fork and that Microsoft keeps control of TypeScript.

How it works

tsrs checks the types in code before the code runs, and the work started at Owner, a restaurant software company. There, Max Schwenk used the Claude Opus model with more than 20 AI agents, which wrote all the code, Schwenk tells. Teams of Cloudflare and VoidZero continue the work.

The numbers

Schwenk tells that a check fell from 80 seconds with the Go compiler to about 7 seconds on a build server. Microsoft tells that ideas from tsrs increase the speed of TypeScript 7.1.

What is not known

The speed figures come from Cloudflare and Schwenk, not from other groups. Schwenk uses the TypeScript tests and a memory check tool, Miri. These tests found one memory bug.

Insight: Cloudflare builds the tools that agents use

GitHub moved its Copilot runtime from TypeScript to Rust, and Cloudflare bought VoidZero in June. At this time Cloudflare leads a fast checker that works in browser sandboxes, where agents write and test code. This reads as a move to control the tools for apps that AI makes, and Microsoft also gets help from it. Builders must monitor if the Oxc toolchain uses tsrs.