Free GZIP Compression Tester - Check Website File Compression

GZIP Compression Tester

Test if your website uses compression for faster loading. Check GZIP, Brotli, and other compression algorithms.

Page Speed Optimization
Test Website Compression

Testing Compression...

Analyzing GZIP, Brotli, and other compression methods.

Initializing compression test...
Compression Performance Score
0
Compression Analysis
Based on compression ratio, algorithm support, and file optimization.
0
Compressed Files
0%
Size Savings
0
Uncompressed
0
Total Files
Scores above 80 are good, above 90 are excellent. Aim for 95+.
Compression Ratio
0%
Average size reduction
Algorithm
GZIP
Browser support
Brotli Support
No
Better compression
Potential Savings
0 KB
With optimization
File Type Original Size Compressed Size Savings Algorithm Status
File Type Size Potential Savings Priority Action
File Type Original Size Compressed Size Savings Impact

Compression Visualization

Optimization Recommendations

Implementation Guide
# Enable compression in .htaccess or Apache config # ============================================= # Enable GZIP compression <IfModule mod_deflate.c> # Compress HTML, CSS, JavaScript, Text, XML and fonts AddOutputFilterByType DEFLATE application/javascript AddOutputFilterByType DEFLATE application/rss+xml AddOutputFilterByType DEFLATE application/vnd.ms-fontobject AddOutputFilterByType DEFLATE application/x-font AddOutputFilterByType DEFLATE application/x-font-opentype AddOutputFilterByType DEFLATE application/x-font-otf AddOutputFilterByType DEFLATE application/x-font-truetype AddOutputFilterByType DEFLATE application/x-font-ttf AddOutputFilterByType DEFLATE application/x-javascript AddOutputFilterByType DEFLATE application/xhtml+xml AddOutputFilterByType DEFLATE application/xml AddOutputFilterByType DEFLATE font/opentype AddOutputFilterByType DEFLATE font/otf AddOutputFilterByType DEFLATE font/ttf AddOutputFilterByType DEFLATE image/svg+xml AddOutputFilterByType DEFLATE image/x-icon AddOutputFilterByType DEFLATE text/css AddOutputFilterByType DEFLATE text/html AddOutputFilterByType DEFLATE text/javascript AddOutputFilterByType DEFLATE text/plain AddOutputFilterByType DEFLATE text/xml # Remove browser bugs (for older browsers) BrowserMatch ^Mozilla/4 gzip-only-text/html BrowserMatch ^Mozilla/4\.0[678] no-gzip BrowserMatch \bMSIE !no-gzip !gzip-only-text/html Header append Vary User-Agent </IfModule> # Enable Brotli compression (Apache 2.4.26+) <IfModule mod_brotli.c> AddOutputFilterByType BROTLI_COMPRESS text/html text/plain text/xml text/css text/javascript application/javascript application/x-javascript application/json application/xml application/rss+xml application/atom+xml image/svg+xml </IfModule> # Set compression level (1-9, 6 is default) DeflateCompressionLevel 6 # Enable caching for compressed files <IfModule mod_expires.c> ExpiresActive On ExpiresByType text/css "access plus 1 year" ExpiresByType application/javascript "access plus 1 year" ExpiresByType image/svg+xml "access plus 1 year" </IfModule>
# Enable compression in nginx.conf # =============================== gzip on; gzip_vary on; gzip_min_length 1024; gzip_proxied any; gzip_comp_level 6; gzip_buffers 16 8k; gzip_http_version 1.1; # Compress these MIME types gzip_types text/plain text/css text/html text/javascript application/javascript application/x-javascript application/json application/xml application/rss+xml application/atom+xml image/svg+xml application/vnd.ms-fontobject application/x-font-ttf font/opentype; # Enable Brotli compression (nginx with ngx_brotli module) brotli on; brotli_comp_level 6; brotli_static on; brotli_types text/plain text/css text/html text/javascript application/javascript application/json application/xml application/rss+xml image/svg+xml; # Don't compress already compressed files gzip_disable "msie6"; # Set cache headers for compressed files location ~* \.(css|js|svg|woff|woff2|ttf|eot)$ { expires 1y; add_header Cache-Control "public, immutable"; }
# Cloudflare Auto Minify & Brotli # =============================== // 1. Enable in Cloudflare Dashboard: // Speed → Optimization → Auto Minify // ✅ JavaScript // ✅ CSS // ✅ HTML // 2. Enable Brotli: // Speed → Optimization → Brotli // ✅ Enable Brotli // 3. Enable Polish (image optimization): // Speed → Optimization → Polish // ✅ Lossy or Lossless // Using Cloudflare Workers for custom compression: async function handleRequest(request) { let response = await fetch(request); // Only compress text-based content const contentType = response.headers.get('content-type'); const compressibleTypes = [ 'text/html', 'text/css', 'application/javascript', 'application/json', 'application/xml', 'image/svg+xml' ]; if (compressibleTypes.some(type => contentType.includes(type))) { // Cloudflare automatically applies Brotli or GZIP // based on Accept-Encoding header const newHeaders = new Headers(response.headers); newHeaders.set('Vary', 'Accept-Encoding'); return new Response(response.body, { status: response.status, statusText: response.statusText, headers: newHeaders }); } return response; } // 4. Enable Rocket Loader for JavaScript optimization // Speed → Optimization → Rocket Loader // ✅ Automatic
// WordPress GZIP Compression // ======================== // Method 1: Using .htaccess (for Apache) // Add the Apache code above to your .htaccess file // Method 2: Using wp-config.php function enable_gzip_compression() { if (substr_count($_SERVER['HTTP_ACCEPT_ENCODING'], 'gzip')) { ob_start('ob_gzhandler'); } else { ob_start(); } } add_action('init', 'enable_gzip_compression'); // Method 3: Using WordPress Plugins // Recommended plugins: // 1. WP Rocket (Premium) - Best optimization plugin // 2. W3 Total Cache (Free) - GZIP compression option // 3. Autoptimize (Free) - CSS/JS optimization + GZIP // 4. LiteSpeed Cache (Free) - With LSCache server // Method 4: For Nginx servers, use server config above // Disable GZIP in certain cases function disable_gzip_for_specific_pages() { if (is_admin()) { remove_action('init', 'enable_gzip_compression'); } } add_action('init', 'disable_gzip_for_specific_pages', 1); // Combine with other optimizations function optimize_wordpress() { // Remove query strings from static resources function remove_query_strings($src) { if (strpos($src, '?ver=')) { $src = remove_query_arg('ver', $src); } return $src; } add_filter('style_loader_src', 'remove_query_strings', 10, 2); add_filter('script_loader_src', 'remove_query_strings', 10, 2); } add_action('init', 'optimize_wordpress');
// Node.js Express Compression // ========================== const express = require('express'); const compression = require('compression'); const app = express(); // Enable GZIP compression with options app.use(compression({ // compression level (0-9, 6 is default) level: 6, // Filter function to decide what to compress filter: (req, res) => { if (req.headers['x-no-compression']) { // don't compress responses with this header return false; } // fallback to standard filter function return compression.filter(req, res); }, // Threshold (bytes) - only compress responses larger than this threshold: 1024 })); // For Brotli compression (Node.js 10.16.0+) // npm install shrink-ray-current const shrinkRay = require('shrink-ray-current'); app.use(shrinkRay()); // Or use custom compression middleware app.use((req, res, next) => { const acceptEncoding = req.headers['accept-encoding']; if (!acceptEncoding || acceptEncoding.includes('identity')) { return next(); } if (acceptEncoding.includes('br')) { // Brotli compression res.setHeader('Content-Encoding', 'br'); res.setHeader('Vary', 'Accept-Encoding'); } else if (acceptEncoding.includes('gzip')) { // GZIP compression res.setHeader('Content-Encoding', 'gzip'); res.setHeader('Vary', 'Accept-Encoding'); } else if (acceptEncoding.includes('deflate')) { // Deflate compression res.setHeader('Content-Encoding', 'deflate'); res.setHeader('Vary', 'Accept-Encoding'); } next(); }); // Serve static files with compression app.use(express.static('public', { setHeaders: (res, path) => { // Set cache headers for static files if (path.endsWith('.css') || path.endsWith('.js')) { res.setHeader('Cache-Control', 'public, max-age=31536000'); } } })); app.listen(3000, () => { console.log('Server running with compression enabled'); });

Why GZIP Compression is Critical for Website Performance

GZIP compression reduces file sizes by 70-90% for text-based content, making websites load significantly faster. According to Google, pages that load within 2 seconds have an average bounce rate of 9%, while pages taking 5 seconds have a bounce rate of 38%.

Compression directly impacts Core Web Vitals, particularly Largest Contentful Paint (LCP) and First Contentful Paint (FCP). Google has confirmed that page speed is a ranking factor, and compressed resources contribute to better search engine visibility.

Understanding Compression Algorithms

1. GZIP (GNU Zip) - The Standard

Compression Ratio: 70-90% for text files, 30-50% for already compressed files (images, PDFs)

Browser Support: 99.5% of browsers (all modern browsers since 2000)

Best For: HTML, CSS, JavaScript, JSON, XML, SVG, fonts

Not For: Already compressed files (JPEG, PNG, MP4, PDF, ZIP)

2. Brotli - The Modern Alternative

Compression Ratio: 20-26% better than GZIP for text files

Browser Support: 96% of browsers (Chrome, Firefox, Edge, Opera, Safari 11+)

Best For: Static content with pre-compression, HTTPS sites

Unique Feature: Better compression for UTF-8 text, dictionary-based approach

3. Deflate - Legacy Algorithm

Compression Ratio: Similar to GZIP but with implementation issues

Browser Support: Universal but problematic

Recommendation: Avoid - use GZIP instead

Compression Impact by File Type

File Type Average Size Compressed Size Savings Priority
HTML 50KB 10KB 80% Critical
CSS 100KB 20KB 80% Critical
JavaScript 200KB 40KB 80% Critical
JSON/XML 30KB 6KB 80% High
SVG 15KB 3KB 80% Medium
Fonts (TTF/WOFF) 150KB 60KB 60% Medium
Images (JPEG/PNG) 100KB 98KB 2% Low

How Compression Affects Core Web Vitals

1. Largest Contentful Paint (LCP)

Impact: High - Compressed resources load faster, reducing LCP time

Goal: Under 2.5 seconds

How Compression Helps: Reduces transfer time for critical resources (HTML, CSS, render-blocking JS)

2. First Input Delay (FID)

Impact: Medium - Smaller JavaScript files parse and execute faster

Goal: Under 100 milliseconds

How Compression Helps: Reduces JavaScript bundle size, improving parse/compile time

3. Cumulative Layout Shift (CLS)

Impact: Indirect - Faster loading fonts and CSS reduce layout shifts

Goal: Under 0.1

How Compression Helps: Fonts and CSS load faster, preventing FOIT/FOUT

Common Compression Mistakes and Solutions

1. Double Compression

Problem: Compressing already compressed files (JPEG, PNG, PDF)

Symptoms: CPU waste, minimal size reduction, potential corruption

Solution: Configure server to only compress text-based files

2. Missing Vary: Accept-Encoding Header

Problem: CDN/proxy serves compressed content to non-supporting browsers

Symptoms: Broken rendering in older browsers

Solution: Always include Vary: Accept-Encoding header

3. Wrong Compression Level

Problem: Level 9 (maximum) causes high CPU usage with minimal benefit

Symptoms: Slow server response, high CPU load

Solution: Use level 6 for dynamic content, level 9 for static pre-compressed

4. No Brotli for Static Content

Problem: Missing 20-26% additional compression from Brotli

Symptoms: Larger file sizes than necessary

Solution: Pre-compress static files with Brotli during build process

Advanced Compression Techniques

1. Pre-compressed Static Files

Generate compressed versions during build:

# Generate Brotli and GZIP versions brotli --quality 11 --input style.css --output style.css.br gzip --keep --best --force style.css # Nginx config to serve pre-compressed location ~ \.css$ { brotli_static on; gzip_static on; }

2. Dictionary Compression for Brotli

Create custom dictionary for your specific content patterns:

# Create dictionary from your website's text find . -name "*.html" -o -name "*.css" -o -name "*.js" | \ xargs cat | \ brotli --quality 11 --output dictionary.br # Use dictionary for better compression brotli --quality 11 --dictionary dictionary.br --input file.js

3. Adaptive Compression Based on Network

Serve different compression based on connection type:

// Detect connection type const connection = navigator.connection || navigator.mozConnection || navigator.webkitConnection; if (connection) { if (connection.effectiveType === 'slow-2g' || connection.effectiveType === '2g') { // Use higher compression for slow connections request.headers.set('Accept-Encoding', 'br, gzip;q=0.9'); } else { // Use balanced compression for fast connections request.headers.set('Accept-Encoding', 'br, gzip'); } }

Compression Benchmarks

Real-world performance improvements from compression:

Amazon
100ms faster load = 1% revenue increase
Google
500ms delay = 20% traffic drop
Walmart
1s faster = 2% conversion increase
BBC
1s slower = 10% users leave

Frequently Asked Questions (FAQ)

Does GZIP compression affect SEO rankings?

Yes, indirectly but significantly. Google considers page speed as a ranking factor, and compression improves loading times. Faster pages have lower bounce rates, higher engagement, and better Core Web Vitals scores - all of which affect SEO. Google's own PageSpeed Insights tool specifically checks for compression.

Should I compress images with GZIP?

No, images (JPEG, PNG, WebP) are already compressed using specialized algorithms. GZIP compression on images typically yields less than 5% size reduction while using significant CPU resources. Instead, optimize images by:

  • Using modern formats (WebP, AVIF)
  • Proper compression settings (quality 75-85 for JPEG)
  • Responsive images with srcset
  • Lazy loading below the fold

What's the optimal GZIP compression level?

For dynamic content (HTML, API responses): Level 4-6 provides good balance between compression and CPU usage. For static content (CSS, JS, fonts): Level 9 (maximum) for pre-compressed files. Higher levels provide diminishing returns: Level 6 is about 90% as effective as level 9 but uses significantly less CPU.

How do I test if compression is working?

Multiple methods:

  1. Use this GZIP Compression Tester tool
  2. Browser Developer Tools → Network tab → check "Content-Encoding" header
  3. Command line: curl -H "Accept-Encoding: gzip" -I https://example.com
  4. Online validators: GIDZipTest, CheckGZIP.com
  5. Google PageSpeed Insights or Lighthouse audits
Test with different file types and ensure the "Vary: Accept-Encoding" header is present.