GZIP & Brotli Compression Test Tool Online

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Check whether your site uses GZIP or Brotli compression. See transfer savings, compression status, and compression headers and estimated savings where response-size evidence is available.

Enter a URL to test compression:

How the Compression Test Works

The API fetches your page with browser-like compression support and reads the response headers.

  1. Safe URL check, the host is validated before the server requests it.
  2. Compression request, the fetch includes gzip, deflate, and br in Accept-Encoding.
  3. Header analysis, the content-encoding and content-length headers are read from the response.
  4. Savings estimate, the decoded body size is compared with compressed transfer size when available.

Why Compression Matters

Text compression is one of the simplest speed wins for HTML, CSS, and JavaScript.

  • Faster first load, smaller files reach visitors sooner on mobile networks.
  • Better crawl efficiency, search engines and AI crawlers can retrieve pages with less bandwidth.
  • Lower hosting cost, compressed responses reduce data transfer from your server or CDN.
  • Better Core Web Vitals support, smaller render-blocking CSS and JavaScript can improve LCP and INP.

Compression Encoding Comparison

EncodingBest forNotes
brHTML, CSS, JSOften useful for text; compare actual output and CPU cost rather than assuming a fixed savings ratio.
gzipHTML, CSS, JSUniversal fallback with strong savings.
noneAlready compressed assetsReview larger uncompressed text responses; already-compressed images and WOFF2 fonts usually gain little.

For a wider performance audit, use our website speed optimization guide.

Next steps

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GZIP and Brotli Compression: FAQ

What does the compression test request and report?
It requests the URL while advertising Brotli, GZIP, and deflate support, then reports the final URL, HTTP status, Content-Encoding header, available compressed size, decoded response size, and estimated byte savings.
What counts as compression enabled in this result?
The tool marks compression enabled when the response Content-Encoding is br or gzip. If a server returns no encoding or another value, review the reported header directly and test from the browser or CDN edge used by your visitors.
Why can the result show zero savings or equal sizes?
The decoded body size can be measured after download, but the transferred compressed size depends on the Content-Length header. When that header is absent, such as with streaming or chunked responses, the tool cannot calculate the transfer savings and uses the decoded size as its fallback.
Does this test check every asset on the page?
No. It checks the response for the single URL you submit. Test important HTML pages and direct CSS, JavaScript, JSON, SVG, or font URLs separately because each resource can have different CDN and server compression rules.
Which response is tested when the URL redirects?
The request follows redirects and reports the final URL and its response. If you need to audit both the redirect response and destination, inspect the redirect separately with an HTTP header tool and run this test on the destination URL.
How should I fix an uncompressed text response?
Enable Brotli or GZIP for compressible MIME types in the CDN, hosting platform, or web server, keep a Vary: Accept-Encoding response where applicable, and retest the exact production resource. Avoid recompressing image and video formats that are already compressed.
Why might the compression test fail?
The URL must be publicly reachable. DNS errors, connection failures, timeouts, blocked automated requests, invalid certificates, or a server response outside the tool's limit can prevent a result. A CDN may also vary behavior by location or request headers.
What data is sent when I run the test?
The public URL is sent to Web Aloha's tool endpoint, which requests that resource to inspect its response headers and decoded body size. Do not submit private, signed, or tokenized URLs that should not be fetched by an external service.

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