Page Speed: Enable gzip compression More Recommendations

Rule Summary

Server
High
Easy
74%

Overview

Compressing resources with gzip or deflate can reduce the number of bytes sent over the network.

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Details from Google

Most modern browsers support data compression for HTML, CSS, and JavaScript files. This allows content to be sent over the network in more compact form and can result in a dramatic reduction in download time.

Many web servers can compress files in gzip format before sending them for download, either by calling a third-party module or using built-in routines. To enable compression, configure your web server to set the Content-Encoding header to gzip format for all compressible resources. You can also use deflate, which uses the same compression algorithms, but it is not widely used, so we recommend gzip. If streaming compression imposes too much load on your server, you can usually configure it to pre-compress files and cache them for future downloading.

Note that gzipping is only beneficial for larger resources. Due to the overhead and latency of compression and decompression, you should only gzip files above a certain size threshold; we recommend a minimum range between 150 and 1000 bytes. Gzipping files below 150 bytes can actually make them larger.

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Write your web page content to make compression most effective

To ensure that your content compresses well, do the following:

  • Ensure consistency in HTML and CSS code. To achieve consistency:
    • Specify CSS key-value pairs in the same order where possible, i.e. alphabetize them.
    • Specify HTML attributes in the same order , i.e. alphabetize them. Put href first for links (since it is most common), then alphabetize the rest. For example, on Google's search results page, when HTML attributes were alphabetized, a 1.5% reduction in the size of the gzipped output resulted.
    • Use consistent casing, i.e. use lowercase wherever possible.
    • Use consistent quoting for HTML tag attributes, i.e. always single quote, always double quote, or no quoting at all where possible.
  • Minify JavaScript and CSS. Minifying JavaScript and CSS can enhance compression both for external JS and CSS files and for HTML pages containing inlined JS code and style blocks.
Don't use gzip for image or other binary files

Image file formats supported by the web, as well as videos, PDFs and other binary formats, are already compressed; using gzip on them won't provide any additional benefit, and can actually make them larger. To compress images, see Optimize images.

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