SEO glossary
CDN
A CDN, or content delivery network, is a set of servers spread across the world that hold copies of your files and serve each visitor from a nearby one.
The problem it solves is distance. A request to a single server in Frankfurt takes noticeably longer from Sydney than from Berlin, and no amount of code optimisation removes the round trip. A CDN shortens the trip rather than the work.
It helps most with static files — images, CSS, JavaScript, fonts — and with absorbing traffic spikes. It helps least with a slow database query, because the dynamic response still has to come from your origin. If your time to first byte is bad because the application is slow, a CDN moves the waiting rather than removing it.
Two SEO side effects are worth knowing. A misconfigured CDN can serve stale pages to crawlers long after you have fixed something, and one that treats Googlebot as suspicious traffic can rate-limit or challenge it — which looks exactly like a site that has become uncrawlable.
Definitions are the easy part
The free plan opens every tool with 500 credits and no card, so you can see these numbers on your own site rather than in an example.
Start free