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One problem with the previous integrations was that postcss was called on every page doing the same thing every time.

It would be much better to run postcss once.

Final Integration #

After working on the eleventy site for a while I got this idea from esbuild implementation & my previous post on using a transform.

Putting these together I thought why not use eleventy.before to run postcss to output a minified css file (like esbuild) then use a transform to inject styles into head (see previous post).

📝Postcss 11ty Integration Update (Using a Transform)

📝Using Esbuild With Eleventy (eleventy.before)

Running Postcss Once #

Here is the eleventy.before section.

  // Run postcss (insert css to html later)
  eleventyConfig.on('eleventy.before', async () => {
    const cssInput = fs.readFileSync('src/_styles/_global.css', {
      encoding: 'utf-8',
    const cssOutDir = 'src/_assets/css/'
    const cssOutFile = 'styles.css'
    const cssOutput = cssOutDir + cssOutFile
    if (!fs.existsSync(cssOutDir)) {
      fs.mkdirSync(cssOutDir, { recursive: true })
    const minified = await postcss([tailwindcss(), autoprefixer()])
      .process(cssInput, { from: undefined })
      .then((r) => {
        fs.writeFile(cssOutput, r.css, (err) => {
          if (err) throw err
          console.log(`[11ty] Writing Postcss Output: ${cssOutput}`)
    return minified

Inject CSS Using Transform #

Here is the transform section.

  // PostCSS transform
  eleventyConfig.addTransform('postcss', function (content) {
    if (this.page.outputPath && this.page.outputPath.endsWith('.html')) {
      const minCSS = fs.readFileSync('src/_assets/css/styles.css', {
        encoding: 'utf-8',
      content = content.replace('</head>', `<style>${minCSS}</style></head>`)
    return content

Speed Improvement #

Speed wise this is a lot faster.

[11ty] Copied 11 files / Wrote 27 files in 0.79 seconds (29.3ms each, v2.0.1)
[11ty] Benchmark    896ms  33%    25× (Configuration) "postcss-trans" Transform
[11ty] Copied 11 files / Wrote 25 files in 2.39 seconds (95.6ms each, v2.0.1)
[11ty] Benchmark    977ms  34%    23× (Configuration) "postcss" Nunjucks Async Filter
[11ty] Copied 11 files / Wrote 26 files in 2.61 seconds (100.4ms each, v2.0.1)

📝Integrating Tailwindcss With Eleventy | 📝Postcss 11ty Integration Update

Source Code #

The source for my 11ty blog is available on github.