Title: Brotli Author: Kriko Published: Feb 3, 2021 Last modified: Jul 15, 2026 --- 1. [Home](https://kriko.io/) / 2. [Glossary](https://kriko.io/glossary) / 3. B Letter # Brotli **Brotli** is a lossless compression algorithm that allows text-based resources used on websites to be transferred in smaller sizes. Developed by Google, Brotli is commonly used in HTTP content compression with the `br` content encoding. It helps send resources such as HTML, CSS, JavaScript, JSON, SVG and some font files to the browser in smaller sizes. As a result, page loading performance can improve and the amount of data transferred from the server to the user can decrease. Brotli serves a similar purpose to GZIP, but in many scenarios it can provide better compression ratios than GZIP. According to a comparison shared on web.dev, Brotli can produce files that are approximately 14% smaller for JavaScript, 21% smaller for HTML and 17% smaller for CSS compared with GZIP. These ratios do not have to be the same for every website or every file type; the content of the file, compression level, server configuration and use of pre-compression can affect the result. The main benefit of Brotli is that it allows some of the resources that build a page to be transferred with less data. When file size decreases, the browser can download the relevant resources faster, especially for users on mobile connections or low-bandwidth networks. This can contribute to page loading speed, user experience and, indirectly, some Core Web Vitals metrics. However, Brotli alone does not make a website fast; image optimization, server response time, JavaScript load, caching and rendering performance should also be considered together. It is not correct to treat Brotli as an image or video compression tool. Formats such as JPEG, PNG, WebP, AVIF, MP4 and WebM already have their own compression methods. Trying to compress these files again with Brotli usually does not provide meaningful gains and may sometimes create unnecessary processing cost. Brotli is most effective for text-based files and data structures that contain repeated patterns. Brotli is not a protocol that provides secure communication. Secure communication is provided by HTTPS and TLS. Brotli is related to compressing data before it is transferred. In modern browsers, Brotli support is mostly used over HTTPS connections; however, this does not mean that Brotli provides the security. In HTTP, the client indicates which compression algorithms it supports through the `Accept-Encoding` header, while the server indicates the selected encoding through the `Content-Encoding` header. In a simple HTTP compression flow, the browser may send information such as `Accept- Encoding: br, gzip` to the server. If the server supports Brotli and the relevant file is suitable for Brotli compression, it can return the response with the `Content- Encoding: br` header. The browser then decodes this response and processes it as normal HTML, CSS or JavaScript content. The user does not see this process directly; when configured correctly, compression works in the background. One of the differences between Brotli and GZIP lies in their compression structures and efficiency levels. GZIP is a widely used and reliable solution that has been used for many years. Brotli is a newer alternative that can provide higher compression ratios for modern web resources. However, higher Brotli compression levels can create more CPU cost. For this reason, using the highest compression level for dynamic content is not always the best choice. There are two main approaches to Brotli implementation: dynamic compression and static compression. **Dynamic compression** means that the server compresses the response at the time of the request. This method is flexible, but it can create CPU load under heavy traffic. **Static compression** means that files are pre-compressed in `.br` format and kept ready on the server or CDN. Static compression can be more efficient, especially for CSS, JavaScript and static HTML files that do not change frequently. Using a CDN can make it easier to benefit from Brotli effectively. Many modern CDNs can serve Brotli-compressed content to supported browsers. This structure helps files be delivered from servers closer to users and in smaller sizes. As a result, bandwidth usage may decrease and the download time of page resources may be reduced. However, whether Brotli is actually active on the CDN side should be checked through response headers. Brotli’s effect on SEO is indirect, not direct. Smaller resource sizes can improve page speed, and better performance can support user experience. For search engine bots, faster and more efficiently served pages can contribute to crawling processes; however, using Brotli alone does not guarantee better rankings or more crawl budget. SEO performance should be evaluated together with content quality, technical SEO, site architecture, mobile compatibility, page experience and search intent. To test whether Brotli is working correctly, the Network tab in browser developer tools can be used. If the response headers of the relevant HTML, CSS or JavaScript file show `Content-Encoding: br`, Brotli compression is actively being used. Performance tools such as PageSpeed Insights, Lighthouse, WebPageTest or similar platforms can also help analyse compression issues and transfer sizes. One point to consider when using Brotli is avoiding unnecessary processing on very small files or files that are already compressed. Compression gains may be limited for very small files. Brotli usually does not provide meaningful benefits for already compressed formats such as images, videos and archive files. Therefore, the server or CDN configuration should correctly define which content types will be compressed with Brotli. In summary, **Brotli** is a modern and lossless compression algorithm used to reduce the transfer size of web resources. Compared with GZIP, it can provide better compression ratios for many text-based files. Its most efficient use cases include web resources such as HTML, CSS, JavaScript, JSON, SVG and fonts. 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