Vite Plugin - Optimize CSS Modules

Mangle classnames in production - save up to 30% on css and 90% of build time for free!

Setup

This plugin requires vite of v3 or greater. It only makes sense to use if you're using css modules.

$ npm install --save-dev vite-plugin-optimize-css-modules

In your vite.config.ts simply add the plugin:

import { optimizeCssModules } from 'vite-plugin-optimize-css-modules';
import { defineConfig } from 'vite';

export default defineConfig({
    plugins: [
        optimizeCssModules()
    ]
})

And that's it. When running vite build your generated CSS should be significantly smaller.

Benchmarks

Benchmarks are done against bootstrap and materialize.css assuming all the classes are used as css modules. The benchmark code is located in the benchmarks directory.

Run them by building the plugin via npm run build and then running npm run benchmarks. The results below are from a MacBook Air M2 with node v22.8.0.

Input	Build Time	Gzip Size	Brotli Size
bootstrap-5.0.2.module.css	525ms (-94.06% / -8311ms)	21.3 kB (-26.53% / -7.69 kB)	21.3 kB (-27.54% / -6 kB)
materialize-1.0.0.module.css	572ms (-92.59% / -7156ms)	20.1 kB (-19.70% / -4.93 kB)	20.1 kB (-21.33% / -4.3 kB)

How does it work?

By default, when using css modules, you end up with hashes or other long class-names in your bundled css files:

@keyframes _close-card_pzatx_1 {
    /* ...css */
}

._card_pzatx_32 {
    /* ...css */
}

._back_pzatx_49 ._content_pzatx_70 ._close_pzatx_74 {
    /* ...css */
}

By using this module, the smalles possible classname will be used for each "id":

@keyframes a {
    /* ...css */
}

.v {
    /* ...css */
}

.c .s .w {
    /* ...css */
}