Fix: Failed to load PostCSS config (module is not defined) in Vite

Every version of this error starts with the same words, and the part that tells you the cause comes after the second colon. Read that part first.

Which one you have

1. module is not defined in ES module scope

Your package.json has "type": "module", so a .js config is an ES module, and module.exports doesn’t exist there. Newer projects often set "type": "module", while many older guides and plugin READMEs still show module.exports.

// postcss.config.js
export default {
  plugins: {
    autoprefixer: {},
  },
};

2. A plugin in the config isn’t installed

Failed to load PostCSS config (searchPath: C:/project): [Error] Loading PostCSS Plugin failed: Cannot find module 'postcss-nesting'

The config names a plugin that isn’t in node_modules: copied from another project, or removed from package.json without cleaning up the config.

npm i -D postcss-nesting

3. A config you didn’t know existed

This is the one that costs people an afternoon. My project had no PostCSS config and had never used Tailwind, and the build failed anyway:

Failed to load PostCSS config (searchPath: C:/project/app): [Error] Loading PostCSS Plugin failed: Cannot find module 'tailwindcss'

The message names your project folder as the search path. It doesn’t say where the config it loaded actually came from. When a project has no config, Vite keeps searching upward through parent folders, and it had found an old postcss.config.js one level up, in a folder that held a previous project.

It happens with configs left in a home directory, a monorepo root, or a folder you unzip projects into.

node -e "const fs=require('fs'),p=require('path');let d=process.cwd();for(;;){for(const f of fs.readdirSync(d))if(/^(postcss\.config\.(c|m)?(js|ts)|\.postcssrc(\.(json|ya?ml|js|cjs|mjs))?)$/.test(f))console.log(p.join(d,f));const u=p.dirname(d);if(u===d)break;d=u}"

// vite.config.js
export default {
  css: { postcss: {} },
};

If the error mentions Tailwind directly

If Tailwind v4 is installed and your config says tailwindcss: {}, the error is different and isn’t wrapped in “Failed to load PostCSS config”:

[postcss] It looks like you're trying to use `tailwindcss` directly as a PostCSS plugin.

That one has its own fix: trying to use tailwindcss directly as a PostCSS plugin. The quick way to tell them apart: Cannot find module 'tailwindcss' means Tailwind isn’t installed where the config expects it; “trying to use tailwindcss directly” means it is installed, but it’s v4.

What didn’t work

How this was tested

A fresh Vite 8.3.0 project with "type": "module" on Node 24.14.0, built with vite build. Each cause was produced on purpose: a module.exports config, a config naming an uninstalled plugin, and an app with no config under a parent folder holding an old Tailwind config. Tailwind 4.3.3 was installed only for the last comparison. Every error and every fix above is the real build output.