Enable Compression

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.

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