Server compression checker

What the server compression checker does

This tool requests a webpage and examines the response to determine whether compression is applied. It reports the content encoding used, such as gzip, Brotli, or none.

Compression reduces the number of bytes transferred between the server and the browser. Text-based resources, including HTML, CSS, and JavaScript, can often be compressed to a fraction of their original size. The browser decompresses the response transparently, so the user sees no difference except faster delivery.

Why compression matters

Transfer size directly affects load time, especially on slow or metered connections. Compression is one of the simplest performance improvements available: enabling gzip or Brotli can significantly reduce the bytes sent without changing page content. It also reduces bandwidth costs for the site owner.

Modern browsers advertise their supported encodings through the Accept-Encoding request header. The server responds with a matching Content-Encoding header. Brotli generally compresses text better than gzip, but gzip remains widely supported and effective.

How to interpret the result

If the reported content encoding is gzip or Brotli, compression is active for that response. If no encoding is reported, the response is likely sent uncompressed. Check whether the resource is already compressed by nature, such as an image or video file; recompressing those rarely helps and can even increase size.

Compression behavior can vary by file type and by server or CDN configuration. Test representative resources: an HTML page, a CSS file, and a JavaScript file. If some are compressed and others are not, the configuration likely has gaps by MIME type.

Common compression issues

• Compression disabled. The server sends uncompressed text responses.
• Partial MIME coverage. HTML is compressed but CSS or JavaScript is not.
• Double compression. Already-compressed files are compressed again, sometimes increasing size.
• Proxy or CDN overrides. An intermediary may strip or alter the encoding.
• Dynamic content missed. Some setups compress static files but not generated responses.

Practical workflow

Check the main document and key assets. If compression is missing, review server configuration or CDN settings for gzip or Brotli support. Enable compression by MIME type, and avoid applying it to formats that are already compressed. Re-test after changes and monitor transfer sizes over time.

Limitations

The checker reports the content encoding on the response it receives. CDNs and proxies may change behavior, and the result may not reflect how other resource types are served.