Performance Tools

GZIP Compression Checker

Check whether a website serves compressed (GZIP/Brotli) content.

Enter a domain to check whether it serves compressed content.

More Performance Tools

Image Optimization Checker Brotli Compression Checker Render-Blocking Resources Checker HTTP Version Checker Performance Health Score Cache Headers Checker CDN Detection Keep-Alive Checker

JustChecker tracks your website's performance signals continuously.

What Is the GZIP Compression Checker?

Text files such as HTML, CSS and JavaScript can be compressed before sending, often to a quarter of their size. This tool requests a page and checks whether the server returns it compressed with GZIP or Brotli.

When to Use It

When pages load slowly.
After changing web server or hosting configuration.

How to Use It

Enter the domain.
Check whether compression is enabled.

Understanding the Result

Content-Encoding: gzip or br means compression works. If it is off, enable mod_deflate (Apache), gzip on (Nginx), or compression in your CDN.

Limitations

The check covers the page's HTML; stylesheets and scripts should be compressed too. Images such as JPG and WebP are already compressed and gain nothing. See the Brotli Compression Checker for the newer format.

Frequently Asked Questions

Text-based content (HTML, CSS, JavaScript) typically compresses to 60-80% smaller with GZIP, meaningfully reducing transfer time, especially for visitors on slower connections.

Most modern web servers support it, but it sometimes needs explicit configuration (a module or directive) that's occasionally overlooked, particularly on older server setups or custom-configured infrastructure.

Not meaningfully - image formats like JPEG and PNG are already compressed internally, so applying GZIP on top provides negligible additional benefit and is generally not applied to them by well-configured servers.

It requires a small amount of extra CPU time on the server to compress each response - for virtually all real-world traffic levels this is a worthwhile trade for the bandwidth and load-time savings, but very high-traffic sites sometimes tune compression levels to balance the two.

They check for different compression algorithms - GZIP is the older, universally-supported standard; Brotli is newer and generally achieves better compression ratios, but isn't supported by every legacy client.

Indirectly, through page speed - faster-loading pages tend to perform better on Core Web Vitals and page-experience signals, both of which factor into modern search ranking.