Enable Compression

AI-generated Key Takeaways

• This documentation applies to a deprecated version of PageSpeed Insights (v4) and will be shut down soon; users should refer to the latest version (v5).

• The primary focus of this document is to explain how enabling GZIP compression can significantly improve website performance by reducing file sizes.

• PageSpeed Insights may report compression issues due to interference from proxy servers or anti-virus software affecting the headers returned to the client.

• Modern browsers inherently support GZIP compression, so enabling it on your web server is crucial for optimization.

• This page offers guidance and links to resources on how to enable GZIP compression for various web servers like Apache, Nginx, and IIS.

Deprecated. This page was written for version 4 of the PageSpeed Insights API, which is deprecated and will be shut down in May 2019. Version 5 is the latest and provides both real-world data from the Chrome User Experience Report and lab data from Lighthouse.

This rule triggers when PageSpeed Insights detects that compressible resources were served without gzip compression.

Overview

All modern browsers support and automatically negotiate gzip compression for all HTTP requests. Enabling gzip compression can reduce the size of the transferred response by up to 90%, which can significantly reduce the amount of time to download the resource, reduce data usage for the client, and improve the time to first render of your pages. See text compression with GZIP to learn more.

Recommendations

Enable and test gzip compression support on your web server. The HTML5 Boilerplate project contains sample configuration files for all the most popular servers with detailed comments for each configuration flag and setting: find your favorite server in the list, look for the gzip section, and confirm that your server is configured with recommended settings. Alternatively, consult the documentation for your web server on how to enable compression:

• Apache: Use mod_deflate
• Nginx: Use ngx_http_gzip_module
• IIS: Configure HTTP Compression

FAQ

PageSpeed Insights reports that many of my static content files need to be gzipped, but I have configured my web server to serve these files using gzip compression. Why is PageSpeed Insights not recognizing the compression?

Proxy servers and anti-virus software can disable compression when files are downloaded to a client machine. PageSpeed Insights' results are based on headers that were actually returned to your client, so if you are running the analysis on a client machine that is using such anti-virus software, or that sits behind an intermediate proxy server (many proxies are transparent, and you may not even be aware of a proxy intervening between your client and web server), they may be the cause of this issue.

Feedback

Was this page helpful?

Yes

Great! Thank you for the feedback. If you have a specific, answerable question about using PageSpeed Insights, ask the question in English on Stack Overflow. For general questions, feedback, and discussion, start a thread in the mailing list.

No

Sorry to hear that. If you have a specific, answerable question about using PageSpeed Insights, ask the question in English on Stack Overflow. For general questions, feedback, and discussion, start a thread in the mailing list.