CDN

CDN in plain English

A CDN, or content delivery network, is a network of servers in many locations that stores copies of your site's files and serves them from a location close to each visitor. CDNs can speed up loading, absorb traffic spikes and provide security features such as protection against some attacks. Many hosts and website platforms include one.

How to check a CDN on your site

Ask your host or developer whether you use a CDN. If you do, check its security settings allow verified search engine bots. Use Search Console's Crawl stats and the URL Inspection live test to confirm Googlebot can fetch pages. After updating a page, check the live version updates, which shows whether caching is behaving.

A worked example

A craft shop turns on its CDN's strictest bot protection after a spam attack. Soon, Search Console shows crawl errors. The protection is challenging Googlebot too. Adjusting the settings to allow verified search engine crawlers restores normal crawling, while the protection still blocks the spam.

Where it usually goes wrong

• Blocking search engine crawlers with bot protection.
• Caching pages that should change, such as stock or prices, for too long.
• Assuming a CDN fixes slow page code.
• Forgetting the CDN when diagnosing odd errors.

Why a small site should care

A UK business serving UK customers from a decent UK host may not see dramatic gains from a CDN, but it can still help with images and resilience. The bigger SEO risk is misconfiguration: aggressive bot protection on a CDN can block Googlebot, and caching can serve outdated pages after you update them.

It's also part of how your site copes with sudden interest, such as a mention on local TV or a viral post. A CDN can keep the site up when a basic host on its own might struggle.

Connected technical terms

• LCP: Largest Contentful Paint: how quickly the main content of a page loads.
• Core Web Vitals: Google user-experience metrics: LCP, INP and CLS.
• HTTPS: Encrypted HTTP: expected for modern sites.