Gzip / Brotli Compression

Also Known As

TL;DR

Explanation

Gzip and the newer Brotli algorithm compress HTTP response bodies before transmission, reducing bandwidth and improving load times — HTML, CSS, and JS typically compress by 60–90%. In PHP applications, compression can be applied by the web server (Nginx gzip, Apache mod_deflate) rather than in PHP itself (avoid ob_gzhandler as it conflicts with streaming and partial content). Enable compression for text-based MIME types (text/html, text/css, application/json), exclude already-compressed binary formats (images, videos), and set Vary: Accept-Encoding when using compression.

Common Misconception

Why It Matters

Common Mistakes

• Not enabling gzip for text responses (HTML, CSS, JS, JSON, XML) — the most impactful compression targets.
• Enabling gzip for already-compressed formats (images, video, zipped files) — wastes CPU with no size benefit.
• Using PHP ob_gzhandler() instead of server-level compression — server-level is more efficient.
• Not checking that Content-Encoding: gzip is actually in responses — easy to misconfigure and never notice.

Code Examples

# nginx — gzip not configured:
server {
    # gzip off; (default)
    # All responses sent uncompressed — HTML/CSS/JS 5-10x larger than needed
}

# Correct:
gzip on;
gzip_types text/html text/css application/javascript application/json;
gzip_min_length 1000;

; php.ini — enable zlib output compression
zlib.output_compression = On
zlib.output_compression_level = 6  ; 1-9, 6 is good balance

; Or in nginx (preferred — offloads from PHP)
gzip on;
gzip_vary on;
gzip_min_length 1024;              ; don't compress tiny responses
gzip_types text/plain text/css application/json application/javascript
           text/xml application/xml image/svg+xml;
gzip_comp_level 6;

; Brotli (better compression, HTTPS only)
brotli on;
brotli_types text/plain text/css application/json application/javascript;
brotli_comp_level 6;

References

• ↗ https://developer.mozilla.org/en-US/docs/Web/HTTP/Compression
• ↗ https://nginx.org/en/docs/http/ngx_http_gzip_module.html

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