Text-based resources should be served with compression to minimize total network bytes. The Opportunities section of your Lighthouse report lists all text-based resources that aren't compressed:
How Lighthouse handles text compression
Lighthouse gathers all responses that:
- Have text-based resource types.
- Do not include a
content-encodingheader set tobr,gzip, ordeflate.
Lighthouse then compresses each of these with GZIP to compute the potential savings.
If the original size of a response is less than 1.4KiB, or if the potential compression savings is less than 10% of the original size, then Lighthouse does not flag that response in the results.
How to enable text compression on your server
Enable text compression on the server(s) that served these responses in order to pass this audit.
When a browser requests a resource, it will use the
Accept-Encoding
HTTP request header to indicate what compression algorithms it supports.
Accept-Encoding: gzip, compress, br
If the browser supports Brotli
(br) you should use Brotli because it can reduce the file size of the resources more than the
other compression algorithms. Search for how to enable Brotli compression in <X>, where
<X> is the name of your server. As of December 2022 Brotli is supported in all major browsers except Safari on iOS. See
Browser compatibility
for updates.
Use GZIP as a fallback to Brotli. GZIP is supported in all major browsers, but is less efficient than Brotli. See Server Configs for examples.
Your server should return the
Content-Encoding
HTTP response header to indicate what compression algorithm it used.
Content-Encoding: br
Check if a response was compressed in Chrome DevTools
To check if a server compressed a response:
Press Control+Shift+J (or Command+Option+J on Mac) to open DevTools.
Click the Network tab.
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1. Press Control+Shift+J (or Command+Option+J on Mac) to open DevTools.
2. Click the Network tab.
3. Click the request that caused the response you're interested in.
4. Click the Headers tab.
5. Check the content-encoding header in the Response Headers section.
content-encoding response header.
To compare the compressed and de-compressed sizes of a response:
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1. Press Control+Shift+J (or Command+Option+J on Mac) to open DevTools.
2. Click the Network tab.
3. Enable large request rows.
See Use large request rows.
4. Look at the Size column for the response you're interested in. The
top value is the compressed size. The bottom value is the de-compressed
size.
See also Minify and compress network payloads.
Stack-specific guidance
Joomla
Enable the Gzip Page Compression setting (System > Global configuration > Server).
WordPress
Enable text compression in your web server configuration.