What Is Compression?
Quick Definition
Web compression reduces the size of files transferred between a server and browser by encoding data more efficiently, with gzip and Brotli being the most common algorithms used.
When a browser requests a web page, the server can compress the response before sending it. The browser then decompresses it — this entire process is transparent to users but can reduce transfer sizes by 60-90% for text-based files like HTML, CSS, JavaScript, JSON, and SVG.
Gzip has been the standard compression algorithm for the web since the late 1990s. It typically achieves 60-80% compression ratios on text files. Brotli, developed by Google and released in 2015, offers 15-25% better compression than gzip, especially for static content. Most modern browsers support both.
Compression is enabled at the server or CDN level. Most web servers (Nginx, Apache) and cloud platforms (Vercel, Cloudflare, AWS) enable compression by default. The browser signals which compression algorithms it supports via the Accept-Encoding header, and the server responds with the best available option.
Compression works best on text-based formats. Images, videos, and other binary files that are already compressed (JPEG, PNG, MP4, ZIP) don't benefit much from additional compression and may even get slightly larger. These should be optimized using format-specific techniques instead.
Why It Matters
Compression is one of the easiest and most impactful performance optimizations. It requires zero code changes and can reduce page weight by 70% or more. There's essentially no downside — the CPU cost of compression/decompression is negligible compared to the bandwidth savings.
Enabling Brotli compression when available provides a meaningful improvement over gzip with no user-facing tradeoffs.
Real-World Examples
A corporate website's 500KB JavaScript bundle compressed to 95KB with gzip and 80KB with Brotli, loading in 0.5 seconds instead of 3 seconds on mobile
An API response that was 2MB of JSON compressed to 180KB with Brotli, reducing API latency from 4 seconds to under 1 second on 4G connections
A hosting migration accidentally disabled gzip compression, doubling page load times overnight — re-enabling it immediately restored performance
A static site using Brotli pre-compression at build time (instead of on-the-fly) achieved maximum compression ratios while adding zero server CPU overhead
Related Terms
Page Speed
Page speed measures how quickly the content on a web page loads and becomes interactive, directly affecting user experience, search rankings, and conversion rates.
Minification
Minification is the process of removing unnecessary characters from source code — like whitespace, comments, and long variable names — without changing functionality, reducing file size for faster loading.
CDN (Content Delivery Network)
A CDN is a network of geographically distributed servers that delivers web content to users from the server closest to them, reducing load times and improving reliability.
HTTP/2
HTTP/2 is the second major version of the HTTP network protocol that powers the web, offering significant performance improvements over HTTP/1.1 through multiplexing, header compression, and server push.
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