Check GZIP Compression: Free Online Tester

Use this tool to check GZIP compression on any website in seconds. Enter a domain or URL and the checker shows whether the server sends the page compressed with GZIP, Brotli or Deflate, how many bytes compression saves, and which response headers prove it. It is built for site owners, developers and SEOs.

What Is GZIP Compression?

GZIP compression is a method a web server uses to shrink text files before sending them to a browser. The browser unpacks the file on arrival, so visitors see the same page, only sooner. Smaller transfers mean less bandwidth used and faster loading on slow connections.

The process is a negotiation. A browser sends a request that lists the encodings it understands. If the server supports one of them, it compresses the response and adds a Content-Encoding header naming the method. That header is what this checker looks for.

GZIP, Brotli and Deflate

The tool recognizes three encodings. GZIP is the most widely deployed. Brotli is a newer format that usually produces smaller text files than GZIP and is supported by all modern browsers. Deflate is an older method that is rarely used on its own today. Any of the three counts as a compressed response.

Which Files Benefit?

Compression works on text: HTML, CSS, JavaScript, JSON, XML and SVG. JPEG, PNG, WebP, MP4 and PDF files are already compressed, so running them through GZIP saves almost nothing and wastes server effort.

How to Use the GZIP Compression Checker

You can test a site in under a minute with five steps.

1. Type or paste a domain or full page URL into the box that shows the example.com placeholder. A bare domain works, and so does a URL with a path.
2. Click the check button under the box.
3. Wait while the progress screen shows "Checking compression..." and moves through Connecting, Analyzing and Results.
4. Read the status banner. It says either Compression Enabled with the method named after "This website uses", or Not Compressed.
5. Review the size cards, the Server Information section and the Response Headers list (use the toggle to open it), then run the check button again for another URL.

The checker examines the page you enter, so test your most important templates one at a time: the home page, a blog post, a product page and a category page. Each can behave differently when rules are set per path or per content type.

Worked Example: Reading a Real Result

Here is what a typical check looks like, using sample numbers. Say you enter example.com and the tool fetches a home page whose HTML is 100 KB when fully unpacked.

• Status: Compression Enabled, with GZIP as the method.
• Original Size: 100 KB. Compressed: 22 KB.
• Saved: 78 KB. Reduction: 78%.

The reduction is calculated as (original size minus compressed size) divided by original size, times 100. Here that is (100 minus 22) divided by 100, which gives 78%. The gauge ring fills to match, and a result in this range is normal for HTML that is full of repeated tags and class names.

Now suppose the same page returns Not Compressed. The tool still shows what you are missing: it estimates the size the page would reach with maximum GZIP compression. If that estimate is 22 KB on a 100 KB page, you are sending about 78 KB more than necessary on every uncached visit. That gap is your fix list.

How to Read and Act on Your Results

Your result falls into one of two states, and each has a clear next step.

Compression Enabled

This means the server answered with a compression header, so the basic job is done. Check the reduction figure. HTML typically shrinks by well over half when compressed, so a reduction near 70% to 80% is healthy. A very low reduction on a large page can mean the content was already minified heavily or is mostly inline images or encoded data.

If the method says GZIP, consider Brotli as a follow-up. For static text assets it usually gives smaller files, and your host or CDN may offer it as a setting.

Not Compressed

This means no GZIP, Brotli or Deflate header came back for that page. Look at the estimated savings first. A large estimate means fixing this is worth your time. The tips box at the bottom of the results gives the common routes:

• Apache: add a deflate output filter for text/html, text/css and application/javascript in your .htaccess file.
• Nginx: turn on gzip on; and list the text types in your server config.
• WordPress: enable compression in a caching plugin such as WP Rocket, W3 Total Cache or LiteSpeed Cache.
• CDN: many CDNs, including Cloudflare and AWS CloudFront, can compress automatically, so check their settings.

Server Information and Response Headers

The Server Information cards show details such as the server software, response time and status. Open Response Headers to see the raw lines. Look for Content-Encoding to confirm the method and for Vary: Accept-Encoding, which tells caches to store compressed and plain versions separately. For a deeper header review, the HTTP header checker and the HTTP header analyzer go further into caching and security lines.

Who Should Check GZIP Compression, and When?

Anyone responsible for how fast a site loads benefits from a quick compression test. These are the situations where it earns its place:

• After a hosting move: new servers often ship with compression off, and a migration can silently undo it.
• After adding a CDN or proxy: confirm the edge layer still compresses what the origin sends.
• During a speed audit: if a page-speed report says to enable text compression, this confirms the fix worked.
• Before a launch: test staging and production URLs so you do not ship a heavy site.
• For client reports: the before and after size cards make a clear, easy-to-share proof.

Compression is a speed lever, and speed feeds user experience and Core Web Vitals such as Largest Contentful Paint. It will not rescue thin content, but it removes avoidable delay. Pair it with a check on HTTP/2 and HTTP/3 support to see whether the connection itself is modern, and with the code to text ratio checker if your pages carry heavy markup.

Best Practices and Troubleshooting

Most problems come from a handful of repeat mistakes, and each has a simple fix.

Common Mistakes

• Typing a wrong host. If the tool returns an error or an empty page, check the spelling and try the full URL with https. If the site redirects, the tool follows the redirect and measures the final page.
• Testing only the home page. A plugin or rule may compress HTML but skip other content types. Test several page types.
• Compressing images. Do not add JPEG or PNG to your compression rules. Optimize them with proper image formats instead.
• Forgetting tiny files. Compressing a file under about 1 KB can add overhead and save nothing. Most setups skip those on purpose.

If the Result Looks Wrong

You may see Not Compressed even though your plugin says compression is on. Common causes are a cached page served by a layer that strips the header, a CDN setting overriding the origin, or a rule that matches only certain file extensions. Clear your caches, recheck, and compare against the raw headers. If a redirect chain is involved, run the page through the bulk HTTP status checker to see where it lands.

If you see an error message, wait a moment and run the check again. A slow or unreachable site can interrupt the request.

Limitations to Keep in Mind

The checker reports on the single page you enter, not every file the page loads. A compressed HTML document does not prove your CSS and JavaScript files are compressed too, so verify key assets in your browser's network panel. Sizes are measured on the HTML body, and the estimate for uncompressed pages shows potential, not a guarantee of the exact figure your server will produce.

Results reflect one request at one moment. A server under load, a CDN edge location or a logged-in session can behave differently from what the checker sees as a public visitor.

Enter your site's address in the checker above to see whether your pages are compressed, how much they save, and what to change if they are not. For more speed and technical checks, browse the Website Audit and Performance tools.