Introduction

runtime-checker scans JavaScript and TypeScript and reports the oldest runtime versions that support what the code actually uses.

runtime-checker . --summary

Finished in 665ms using oxc (ast parsing) after scanning 307k lines of code.

Runtimes
- Node.js 24.0.0
- Deno 2.8.0
- Bun 1.3.0

Browsers
- Safari 26.0.0
- Chromium 149.0.0
- Firefox 141.0.0

The default scanner parses source with Oxc and checks runtime APIs, JavaScript syntax, module format, and native TypeScript usage. Compatibility data covers Node.js, Deno, Bun, Safari, Chromium, and Firefox.

Scan the code users will execute. For an unbundled library that may be src; for a bundled application it is usually the emitted client or server directory, because transforms and polyfills can change the actual runtime requirement.

The result is evidence for engines.node, deployment targets, browser support, and release notes. It is not a promise that every behavioral difference between runtimes has been modeled, so use the reported minimum alongside the package's real test matrix.