Technical SEO
GZIP Compression
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What is GZIP Compression?
GZIP compression is a server-side technique that compresses text-based files — including HTML, CSS, JavaScript, and XML — before transmitting them over the network, reducing file sizes by up to 70–80%. The browser decompresses the files upon receipt, which is a fast operation, resulting in a net gain in perceived and actual load speed.
Enabling GZIP (or its modern successor Brotli) is typically a one-line server configuration change and is considered a baseline technical SEO best practice. Compressed responses reduce bandwidth consumption, lower TTFB, and speed up total page rendering — all of which positively influence Core Web Vitals. GZIP effectiveness is highest on unminified text files and lowest on already-compressed formats like JPEG or MP4.
Why it matters for SEO
Uncompressed text assets are one of the easiest performance wins to capture. Enabling GZIP requires minimal effort and can shave hundreds of kilobytes from every page response, directly improving load speed metrics that influence both user experience and search rankings.
Example
A browser requests a 300 KB unminified JavaScript file and sends the header Accept-Encoding: gzip, br. If the server responds with Content-Encoding: br or gzip, the file travels over the network in compressed form and the browser decompresses it on arrival. If the response has no Content-Encoding header at all, compression is switched off and every visitor downloads the full uncompressed file. Checking response headers is the quickest way to tell.
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