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Freerange is a zero-API static-analysis tool that automatically deduces numerical…

2026-07-21 · 01:11 UTC ·@_chenglou ·0 min read

Brief

Cheng Lou (@_chenglou) introduced Freerange, a zero-API static tool that deduces numerical ranges to make user interfaces verifiable. He claims it can statically prove TypeScript layout sizing, absence of NaNs/Infinity, and array-bounds safety. Freerange is designed to be drop-in, runtime-free, and RL-friendly, presented as a first step toward proof engineering.

Why it matters

Freerange is a zero-API static-analysis tool that automatically deduces numerical ranges and claims it can prove TypeScript (TS) layouts obey specified sizing, ensure values are free of NaN and Infinity, and keep array indices within bounds.

Key details

  • Announced by @_chenglou on 2026-07-21 as the first step to turn “vibe coding” into proof engineering, Freerange is droppable into any codebase, runs without a browser/runtime, and is described as RL-friendly after “many months & billions of tokens.”
Source evidence

My dear UI developers, ML practitioners, and fans of programming language:

Many months & billions of tokens later, I’m proud to present to you the first step in our long, long collective journey to turn vibe coding onto proof engineering, starting with: making user interfaces verifiable.

Introducing: Freerange, a zero-API tool that automatically deduces your code’s numerical ranges. By doing so, Freerange is able to prove that e.g.:
- your TS layouts obey your specified sizing
- that they’re free of NaNs and Infinity
- that your array indices stay within bounds

All of that, done statically. No browser, no running code, droppable into any codebase, and for the ML folks: RL-friendly