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Compression Headers Analyzer ​

Analyzer IDCategorySeverityTime To Fix
compression-headers⚡ PerformanceMedium30 minutes

What This Checks ​

Verifies that your web server returns compressed responses for static assets like JavaScript, CSS, and HTML files. Recognised encodings are gzip, br (brotli), zstd (zstandard), and deflate.

Checks for:

  • Content-Encoding response header present on JS and CSS assets
  • A recognised compression encoding (gzip, br, zstd, deflate)
  • Correct Accept-Encoding negotiation (brotli is only advertised on HTTPS sites)

Note: Brotli (br) is only negotiated over HTTPS. The analyzer reflects this: brotli is only checked on HTTPS sites.

Why It Matters ​

  • Bandwidth Reduction: Compression reduces transfer size by 60-90% for text-based assets, directly cutting hosting costs
  • Faster Load Times: Smaller files download faster, especially on slow or mobile connections. Gzip cuts JS by ~70%, brotli by ~75%
  • Core Web Vitals: Faster asset delivery improves LCP and FID scores, which affect SEO rankings
  • Production Critical: Uncompressed assets are one of the easiest performance wins to miss in server configuration

How to Fix ​

Quick Fix (5 minutes) ​

Enable gzip in your web server with the minimum required configuration:

Nginx:

nginx
# /etc/nginx/nginx.conf
http {
    gzip on;
    gzip_types text/plain text/css application/javascript application/json image/svg+xml;
    gzip_min_length 1000;
}

Apache:

bash
sudo a2enmod deflate
sudo systemctl restart apache2
apache
# .htaccess or httpd.conf
<IfModule mod_deflate.c>
    AddOutputFilterByType DEFLATE text/html text/css application/javascript application/json
</IfModule>

CDN (no server config needed): Most CDNs compress automatically. Enable "Compress Objects Automatically" in AWS CloudFront, or verify it is on in Cloudflare's Speed settings.

Proper Fix (30 minutes) ​

For full compression coverage including brotli (HTTPS only) and pre-compressed asset serving:

Nginx - gzip + brotli:

nginx
http {
    # Gzip (all connections)
    gzip on;
    gzip_vary on;
    gzip_min_length 1000;
    gzip_comp_level 6;
    gzip_proxied any;
    gzip_types
        text/plain text/css text/javascript
        application/json application/javascript application/x-javascript
        application/xml application/xml+rss
        font/ttf font/otf font/woff font/woff2
        image/svg+xml;

    # Brotli (requires ngx_brotli module — HTTPS only in browsers)
    brotli on;
    brotli_comp_level 6;
    brotli_types
        text/plain text/css text/javascript
        application/json application/javascript application/x-javascript
        application/xml font/ttf font/woff font/woff2
        image/svg+xml;
}

Install brotli module for Nginx:

bash
# Ubuntu/Debian
sudo apt-get install libnginx-mod-brotli

# Alpine (Docker)
apk add --no-cache nginx-mod-http-brotli

Apache - mod_deflate + mod_brotli:

apache
<IfModule mod_deflate.c>
    AddOutputFilterByType DEFLATE text/html text/css
    AddOutputFilterByType DEFLATE text/javascript application/javascript
    AddOutputFilterByType DEFLATE application/json application/xml
    AddOutputFilterByType DEFLATE font/ttf font/woff font/woff2 image/svg+xml
    DeflateCompressionLevel 6
</IfModule>

# Apache 2.4.26+ only
<IfModule mod_brotli.c>
    AddOutputFilterByType BROTLI_COMPRESS text/html text/css
    AddOutputFilterByType BROTLI_COMPRESS text/javascript application/javascript
    AddOutputFilterByType BROTLI_COMPRESS application/json application/xml
    AddOutputFilterByType BROTLI_COMPRESS font/ttf font/woff font/woff2 image/svg+xml
</IfModule>

Serve pre-compressed assets (maximum performance):

Build pre-compressed versions during your asset pipeline:

javascript
// webpack.mix.js
const CompressionPlugin = require('compression-webpack-plugin');

mix.webpackConfig({
    plugins: [
        new CompressionPlugin({ algorithm: 'gzip', test: /\.(js|css|svg)$/ }),
        new CompressionPlugin({ algorithm: 'brotliCompress', test: /\.(js|css|svg)$/, filename: '[path][base].br' }),
    ],
});

Then tell Nginx to serve them directly instead of compressing on the fly:

nginx
location ~* \.(js|css)$ {
    gzip_static on;
    brotli_static on;
}

Verify compression is working:

bash
curl -H "Accept-Encoding: gzip, br" -I https://yoursite.com/js/app.js
# Look for: Content-Encoding: gzip (or br)

ShieldCI Configuration ​

This analyzer is automatically skipped in CI environments ($runInCI = false) and only runs in production and staging environments.

Why skip in CI and development?

  • Compression is a web server configuration and cannot be verified without a running server
  • Local and CI environments typically serve assets without a web server in front of them
  • Production and staging should have a properly configured web server (Nginx, Apache, or CDN)

Environment Detection: The analyzer checks your Laravel APP_ENV setting and only runs when it maps to production or staging. Custom environment names can be mapped in config/shieldci.php:

php
// config/shieldci.php
'environment_mapping' => [
    'production-us' => 'production',
    'production-blue' => 'production',
    'staging-preview' => 'staging',
],

References ​

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