Tailwind with Next.js - Performance & Optimization

Performance: Tailwind with Next.js

MEDIUM IMPACT

This affects page load speed and rendering performance by how CSS is generated, loaded, and applied in Next.js projects using Tailwind.

Including Tailwind CSS in a Next.js project

Tailwind

module.exports = {
  mode: 'jit',
  purge: ['./pages/**/*.{js,ts,jsx,tsx}', './components/**/*.{js,ts,jsx,tsx}'],
  // other config
};

Generates only the CSS classes actually used in the project, reducing CSS size drastically.

📈 Performance GainSaves 150-250kb CSS, reduces render-blocking CSS, improves LCP by 20-40%.

Including Tailwind CSS in a Next.js project

Tailwind

@import 'tailwindcss/base';
@import 'tailwindcss/components';
@import 'tailwindcss/utilities';

// No purge or JIT enabled in tailwind.config.js

Generates a large CSS file with many unused styles, increasing bundle size and slowing initial load.

📉 Performance CostAdds 200-300kb of unused CSS, blocking rendering longer and increasing LCP.

Performance Comparison

Pattern	DOM Operations	Reflows	Paint Cost	Verdict
Tailwind without JIT and purge	Normal DOM	1 reflow per style change	High paint cost due to large CSS	[X] Bad
Tailwind with JIT and purge in Next.js	Normal DOM	1 reflow per style change	Low paint cost due to small CSS	[OK] Good

Rendering Pipeline

Tailwind CSS classes are parsed and compiled during build or runtime (JIT). The resulting CSS is loaded by the browser, then style calculation, layout, paint, and composite happen.

→Style Calculation

→Layout

→Paint

⚠️ BottleneckStyle Calculation due to large CSS files with many unused selectors

Core Web Vital Affected

LCP

This affects page load speed and rendering performance by how CSS is generated, loaded, and applied in Next.js projects using Tailwind.

Optimization Tips

1Always enable Tailwind JIT mode in Next.js for smaller CSS bundles.

2Configure purge paths to remove unused CSS classes from production builds.

3Check CSS file sizes in DevTools Network tab to ensure efficient loading.

Performance Quiz - 3 Questions

What is the main performance benefit of using Tailwind's JIT mode with Next.js?

A It adds more CSS classes to support all possible styles.

B It generates only the CSS classes used, reducing CSS file size.

C It delays CSS loading until after page load.

D It disables CSS animations for faster rendering.

DevTools: Network

How to check: Open DevTools > Network tab > Reload page > Filter by CSS > Check size of CSS files loaded

What to look for: Look for large CSS files (100kb+) indicating unused styles; smaller CSS files indicate good purge/JIT usage.