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News, updates and guides on GTmetrix and general web performance

Adding Custom CDN Hostnames

If you’re sure your website uses a performant and reputable CDN, you can add the hostname to GTmetrix tests to avoid triggering the “Use a CDN” audit.


How Does GTmetrix CDN Detection Work

GTmetrix auto-detects well-known and popular CDNs (e.g., Cloudflare, StackPath, Fastly, etc.) using our custom “Use a Content Delivery Network (CDN)” audit. This also includes third-party services that are known to be delivered on CDNs.

However, we can’t possibly know about all the CDNs in existence since there are hundreds (if not thousands) of CDN services available. If you’re using a CDN we don’t know about yet, GTmetrix may not detect that your page is on a CDN.

If you are confident that your page is using a well-performing global CDN, then follow our guide below.

Note that “Use a Content Delivery Network (CDN)” is a custom GTmetrix Lighthouse audit. Learn more.



Confirm Your CDN Usage

You’ll need to first confirm that your page is in fact on a CDN and has been properly configured.

This step also helps in case you’re using a CDN that is already on our auto-detect list, but still triggering the “Use a CDN” audit.

One way to do this is by checking your Response headers in the Waterfall Chart.

Look for CDN details in your Response headers.

If you see CDN related Response headers, it’s a good sign that your requests are being served via the CDN, and not from the origin server.


Add Your CDN Hostname in User Settings

Before you do this, you should confirm that:

  • GTmetrix is triggering the “Use a CDN” audit for your self-hosted page resources (i.e., not third-party resources from other domains)
  • You’re confident that your global CDN performs well

Once you’ve confirmed your website is using a well-performing and reliable CDN, you can add its hostname to GTmetrix to avoid triggering the “Use a Content Delivery Network (CDN)” audit.
Step 1) Copy the CDN hostname (without http:// or https://)

In the above example, the hostname is

Note that not all hostnames contain the word “cdn”, and they can differ based on how the CDN is implemented. In some cases, the hostname is the same as your website’s domain.
Step 2) Add the CDN hostname to to your Account

Make sure you’re logged into GTmetrix and visit your Account page.

Paste the CDN hostname in the CDN Hostnames field under User Settings.

Add your CDN’s hostname in User Settings on your Account page.

You can add multiple hostnames, just ensure they are one per line.
Step 3) Save your Settings

GTmetrix will now recognize your hostname as a CDN, and will identify resources from that hostname as being on a CDN.

Note that inputted hostnames here will be recognized as a CDN across all your GTmetrix tests.


Is Your CDN Not Being Detected?

You may see that despite being on a CDN that should be auto-detected (e.g., Cloudflare, StackPath, Fastly, etc.), GTmetrix still triggers the “Use a Content Delivery Network (CDN)” audit.

GTmetrix generally looks at Response headers to see if your requests are in fact being served from a known CDN. If they aren’t present, GTmetrix assumes your requests are being served from the origin server, and will flag them as needing a CDN.

To verify this, look at your Response headers – if you don’t find any CDN details, then you’ll need to ensure that your CDN is properly configured to deliver your page resources.

Lack of CDN details in Response headers indicates your CDN may not be properly configured.


Once your CDN has been properly configured, GTmetrix will no longer trigger the CDN audit.



Add Your CDN to the GTmetrix Auto-Detect List

If you are a Global CDN provider and are confident that it performs well, you can submit your CDN to us for testing.

If we find the performance to be satisfactory, we can include it in our CDN auto-detect list.

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