CSS and JS Minifier, a VS Code extension

Overview

A VS Code extension that minifies the CSS or JavaScript file you have open. It started because I was pasting legacy WordPress theme files into a web form to minify them, and it became a published extension with its own test matrix and documentation site.

The minification runs on the machine. CSS goes through LightningCSS and JavaScript through oxc-minify, two Rust libraries, so it works offline, has no file size limit and no rate limit.

The challenge

The first version sent the code to a minification service over the network, so it depended on someone else's server and its limits. Moving to local Rust libraries removed that, but it meant shipping native binaries, one per platform, inside a VS Code extension. The extension then had to keep working across VS Code versions, and a change in VS Code 1.110 broke the test runner on macOS for every extension, mine included.

Key features

• Minify in place or to a new file. Two commands, from the command palette or the context menu. The second writes file.min.css or file.min.js next to the original.
• Size statistics. The percentage saved and the before and after sizes.
• Minify on save, as an option.
• Fully offline, with clear error messages for syntax errors and invalid content.
• Seven languages: English, Spanish, French, German, Portuguese, Japanese and Chinese.
• Six platform packages: Linux x64 and ARM64, macOS Intel and Apple Silicon, Windows x64 and ARM.

Technologies used

• Extension: TypeScript, the VS Code API, VS Code's localization bundles.
• Minification: LightningCSS for CSS, oxc-minify for JavaScript.
• Tooling and infrastructure: GitHub Actions with tests against the minimum supported VS Code, the stable release and Insiders, on macOS, Ubuntu and Windows. CodeQL, Dependabot, and a documentation site, built with docs-sitekit, that rebuilds on every release.

Outcome

Released to the Visual Studio Marketplace, with version 1.3.4 as the latest at the time of writing. The Marketplace page in the cover showed 4,164 installs and a five-star rating on 2026-10-29.

I wrote about three parts of it: moving the minification offline, finding out that six of seven translations were never shown, and the macOS bug that broke every extension's tests, which I fixed upstream in Microsoft's vscode-test.