Failed to load PostCSS config: Failed to load PostCSS config . I checked again and again and got to know that i have to install post css to run my vite react project without it doesnt runs.

[KanhaSahu-dev]

I have to install postcss , then i have to create a postcss.config.js file then only the project runs but isn't vite allows whatever preprocessor we can install and sometimes we dont even need a preprocessor . Is it mandatory??

I also checked other help discussions there people said if tailwindcss module is in the parent directory then running in child may rise to error and they deleted that but in my case i opened a enirely new folder and ran the problem exists as long as the postcss.config.js isnt installed but why ?

PS D:\WEB-SELF-LEARNING\REACT\08miniContext> npm run dev

08minicontext@0.0.0 dev
vite

VITE v5.2.11 ready in 884 ms

➜ Local: http://localhost:5173/
➜ Network: use --host to expose
➜ press h + enter to show help
node:internal/process/promises:289
triggerUncaughtException(err, true /* fromPromise */);
^

[Failed to load PostCSS config: Failed to load PostCSS config (searchPath: D:/WEB-SELF-LEARNING/REACT/08miniContext): [Error] Loading PostCSS Plugin failed: Cannot find module 'tailwindcss'
Require stack:

• D:\postcss.config.js

(@d:\postcss.config.js)
Error: Loading PostCSS Plugin failed: Cannot find module 'tailwindcss'
Require stack:

• D:\postcss.config.js

(@d:\postcss.config.js)
at load (file:///D:/WEB-SELF-LEARNING/REACT/08miniContext/node_modules/vite/dist/node/chunks/dep-cNe07EU9.js:29093:11)
at file:///D:/WEB-SELF-LEARNING/REACT/08miniContext/node_modules/vite/dist/node/chunks/dep-cNe07EU9.js:29118:16
at Array.map ()
at plugins (file:///D:/WEB-SELF-LEARNING/REACT/08miniContext/node_modules/vite/dist/node/chunks/dep-cNe07EU9.js:29117:8)
at processResult (file:///D:/WEB-SELF-LEARNING/REACT/08miniContext/node_modules/vite/dist/node/chunks/dep-cNe07EU9.js:29187:14)
at file:///D:/WEB-SELF-LEARNING/REACT/08miniContext/node_modules/vite/dist/node/chunks/dep-cNe07EU9.js:29317:14]

Node.js v22.1.0

This is my vite.config.js
import { defineConfig } from 'vite'
import react from '@vitejs/plugin-react'

// https://vitejs.dev/config/
export default defineConfig({
plugins: [react()],
})

[vladpereverzyev]

The error isn't Vite forcing you to use PostCSS — it's Vite finding a PostCSS config it can't load.

Look at the stack trace:

Require stack:
- D:\postcss.config.js

There's a postcss.config.js sitting at the root of your D: drive, not in your project. When Vite processes CSS it uses postcss-load-config, which looks for a config starting in your project folder and walking up the directory tree until it finds one. Your project (D:\WEB-SELF-LEARNING\REACT\08miniContext) has no local config, so the search climbs all the way up to D:\postcss.config.js. That stray file references the tailwindcss plugin, which isn't installed there — hence Cannot find module 'tailwindcss'.

That also clears up the two things that confused you:

Is PostCSS mandatory? No. Vite handles CSS out of the box. You don't need PostCSS or a config at all unless you actually want PostCSS plugins (Tailwind, autoprefixer, etc.).
Why does creating a postcss.config.js in the project "fix" it? A config inside your project folder is found first, so the upward search stops there and never reaches the broken D:\ one. That's not fixing the cause, just shadowing it.

The clean fix is to delete (or move) that stray file:

del D:\postcss.config.js

After that your project runs fine with the plain vite.config.js you posted — no PostCSS config needed.

If you do want Tailwind in this project, install it locally and keep its config inside the project instead of at the drive root. Follow the official install guide, since the setup changed in Tailwind v4 (it now uses @tailwindcss/postcss or the dedicated Vite plugin).