What is compression

If you want to send a large file by email, you normally zip it. Using a tool like Winzip, you make the file much smaller. The receiver uses a similar tool to unzip the file and open the original document. Great, you've just sent a smaller file to someone else, without losing any data.

Compressions for your website is very similar: your webserver uses a compression algorithm to reduce the file size of your site. Your browser understands that mechanism, de-compresses it, and shows you the website. The result is smaller files and a faster experience for your visitor.

Using compression can reduce the page size by up to 70%, and it's easy to set up. A quick win to improve your page speed.  

What to compress?

Because it compresses text, it should be used on the following file types:

• HTML
• Javascript
• CSS files
• XML

Don't try to compress images: they'll only get larger because formats like PNG, JPEG, and GIF already include compression. Compress text-based files only

Gzip and Brotli

Two common compression algorithms are Gzip and Brotli. Both do a similar job: reducing the size of a text by up to 70%.

Brotli is relatively new and was developed by Google. It's slightly more efficient and can reduce the file size even more - especially for CSS and Javascript. Because not all browsers support it, it's a good idea to also keep Gzip support on, which is more widely supported.

Unless you want to squeeze out every bit of performance of your server, we recommend you don't spend too much time comparing the two. If only Gzip is enabled on your server, that's normally sufficient.

Most web hosts or CDNs have compression enabled by default. If compression is not enabled, follow the instructions below.

How to enable Gzip compression

Apache Server settings

If you have access to the server configuration file, the following code will enable Gzip for your server.

<IfModule mod_deflate.c>
AddOutputFilterByType DEFLATE text/plain
AddOutputFilterByType DEFLATE text/html
AddOutputFilterByType DEFLATE text/xml
AddOutputFilterByType DEFLATE text/css
AddOutputFilterByType DEFLATE text/javascript
AddOutputFilterByType DEFLATE application/xml
AddOutputFilterByType DEFLATE application/rss+xml
AddOutputFilterByType DEFLATE application/javascript
</IfModule>

.htaccess file

If you can't change the server settings, you can use the same code in your .htaccess file to enable compression.

Nginx

Are you using an Nginx server? You can use this configuration to enable Gzip on your server:

server {
    gzip on;
    gzip_types     text/plain application/xml;
    gzip_proxied     no-cache no-store private expired auth;
    gzip_min_length     1000;

}

More information about Gzip on Nginx

The cost of compression

You might think that compressing and decompressing also take time. That's true, but both the browser and the server are very efficient at this process. The time saved because of the reduced file size far outweighs the extra time it takes to compress and decompress the content.

How do I know if a browser can handle compression?

Browsers let the server know which types of compression it can handle. It uses the accept-encoding request header to tell the server if it can handle Gzip, Brotli, or both. Allmodern browsers support Gzip, and most also know Brotli.

If the browser accepts compressed files, the server will act accordingly and sent a nice and small file to the browser, significantly reducing the load times of your page.