Extracting

UnoCSS works by searching for the utilities usages from your codebase and generate the corresponding CSS on-demand. We call this process extracting.

Content Sources

UnoCSS supports extracting utilities usages from multiple sources:

• Pipeline - Extract right from your build tools pipeline
• Filesystem - Extract from your filesystem by reading and watching files
• Inline - Extract from inline plain text

Usages of utilities that comes from different sources will be merged together and generate the final CSS.

Extracting from Build Tools Pipeline

This is supported in the Vite and Webpack integrations.

UnoCSS will read the content that goes through your build tools pipeline and extract the utilities usages from them. This is the most efficient and accurate way to extract as we only extract the usages that are actually used in your app smartly with no additional file I/O is made during the extraction.

By default, UnoCSS will extract the utilities usage from files in your build pipeline with extension .jsx, .tsx, .vue, .md, .html, .svelte, .astro and then generate the appropriate CSS on demand. .js and .ts files are NOT included by default.

To configure them, you can update your uno.config.ts:

// uno.config.ts
export default defineConfig({
  content: {
    pipeline: {
      include: [
        // the default
        /\.(vue|svelte|[jt]sx|mdx?|astro|elm|php|phtml|html)($|\?)/,
        // include js/ts files
        'src/**/*.{js,ts}',
      ],
      // exclude files
      // exclude: []
    },
  },
})

You can also add @unocss-include magic comment, per-file basis, anywhere in the file that you want UnoCSS to scan. If you need to scan *.js or *.ts files, add them in the configuration to include all js/ts files as scan targets.

// ./some-utils.js

// since `.js` files are not included by default,
// the following comment tells UnoCSS to force scan this file.
// @unocss-include
export const classes = {
  active: 'bg-primary text-white',
  inactive: 'bg-gray-200 text-gray-500',
}

Similarly, you can also add @unocss-ignore to bypass the scanning and transforming for the whole file.

If you want the UnoCSS to skip a block of code without being extracted in any extracting files, you can use @unocss-skip-start @unocss-skip-end in pairs. Note that it must be used in pairs to be effective.

<p class="text-green text-xl">
  Green Large
</p>

<!-- @unocss-skip-start -->
<!-- `text-red` will not be extracted -->
<p class="text-red">
  Red
</p>
<!-- @unocss-skip-end -->

Extracting from Filesystem

In cases that you are using integrations that does not have access to the build tools pipeline (for example, the PostCSS plugin), or you are integrating with backend frameworks such that the code does not go through the pipeline, you can manually specify the files to be extracted.

// uno.config.ts
export default defineConfig({
  content: {
    filesystem: [
      'src/**/*.php',
      'public/*.html',
    ],
  },
})

The files matched will be read directly from the filesystem and watched for changes at dev mode.

Extracting from Inline Text

Additionally, you can also extract utilities usages from inline text, that you might retrieve from elsewhere.

You may also pass an async function to return the content. But note that the function will only be called once at the build time.

// uno.config.ts
export default defineConfig({
  content: {
    inline: [
      // plain text
      '<div class="p-4 text-red">Some text</div>',
      // async getter
      async () => {
        const response = await fetch('https://example.com')
        return response.text()
      },
    ],
  },
})

Limitations

Since UnoCSS works at build time, it means that only statically presented utilities will be generated and shipped to your app. Utilities that are used dynamically or fetched from external resources at runtime might NOT be detected or applied.

Safelist

Sometimes you might want to use dynamic concatenations like:

<div class="p-${size}"></div> <!-- this won't work! -->

Due the fact that UnoCSS works in build time using static extraction, at the compile time it can't possibility know all the combination of the utilities then. For that, you can configure the safelist option.

// uno.config.ts
safelist: 'p-1 p-2 p-3 p-4'.split(' ')

The corresponding CSS will always be generated:

.p-1 { padding: 0.25rem; }
.p-2 { padding: 0.5rem; }
.p-3 { padding: 0.75rem; }
.p-4 { padding: 1rem; }

Or more flexible:

// uno.config.ts
safelist: [
  ...Array.from({ length: 4 }, (_, i) => `p-${i + 1}`),
]

If you are seeking for a true dynamic generation at runtime, you may want to check out the @unocss/runtime package.

Static List Combinations

Another ways to work around the limitation of dynamically constructed utilities is that you can use an object that list all the combinations statically. For example, if you want to have this:

<div class="text-${color} border-${color}"></div> <!-- this won't work! -->

You can create an object that lists all the combinations (assuming you know any possible values of color you want to use)

// Since they are static, UnoCSS will able to extract them on build time
const classes = {
  red: 'text-red border-red',
  green: 'text-green border-green',
  blue: 'text-blue border-blue',
}

And then use it in your template:

<div class="${classes[color]}"></div>

Blocklist

Similar to safelist, you can also configure blocklist to exclude some utilities from being generated. This is useful to exclude some extraction false positives. Different from safelist, blocklist accepts both string for exact match and regular expression for pattern match.

// uno.config.ts
blocklist: [
  'p-1',
  /^p-[2-4]$/,
]

This will exclude p-1 and p-2, p-3, p-4 from being generated.