# Compression — Nginx

Source: https://www.skillbyai.com/en/nginx/c-compress

> Compress responses with gzip and serve pre-compressed files.

## Fewer bytes over the wire

Text responses (HTML, CSS, JavaScript, JSON, SVG) compress very well, often to a fraction of their size, which speeds up page loads, especially on mobile networks. Enable **`gzip on;`** and list compressible **`gzip_types`** (`text/html` is always included); skip already-compressed formats such as JPEG, PNG, WebP and video, which only waste CPU. `gzip_comp_level` trades CPU for size (levels around 4 to 6 are a good balance), `gzip_min_length` skips tiny responses, and `gzip_vary on;` adds `Vary: Accept-Encoding` so caches store compressed and uncompressed variants separately. `gzip_proxied any;` also compresses proxied responses. For static assets, compress at **build time** and enable **`gzip_static on;`** so NGINX serves `app.js.gz` directly without compressing on every request. **Brotli** usually compresses text better than gzip; it is available through the third-party `ngx_brotli` module or prebuilt packages, with `brotli_static` for pre-compressed `.br` files.

## Gzip for dynamic and static content

Compress text types, skip images, serve pre-built .gz files.

```nginx
http {
    gzip on;
    gzip_comp_level 5;
    gzip_min_length 1024;
    gzip_vary on;
    gzip_proxied any;
    gzip_types text/css text/plain text/xml application/javascript
               application/json application/xml image/svg+xml;

    server {
        location /assets/ {
            gzip_static on;          # serve app.3f9a.js.gz if present and accepted
            expires 1y;
            add_header Cache-Control "public, immutable";
        }
    }
}
```

## Vacuum-packing clothes for a trip

Compression is vacuum-packing: text squeezes down enormously, while already-dense items such as images do not shrink, so packing them just wastes effort.

**Quiz:** Which content type should normally NOT be gzip-compressed by NGINX?

- [ ] application/json
- [x] image/jpeg
- [ ] text/css
- [ ] application/javascript

*Answer:* image/jpeg. JPEG is already compressed; gzipping it wastes CPU for no benefit.