CDN (Content Delivery Network)

A CDN is a network of servers distributed worldwide that cache copies of a site's files and serve each visitor from the location nearest them, cutting the distance data travels and therefore load time.

The gain is largest for visitors far from your origin server. A site hosted in India serving a customer in Texas has a round trip of thousands of miles per request; a CDN reduces that to a nearby city.

CDNs cache static assets by default — images, CSS, JavaScript — and can cache full HTML pages when they're static. That second part is where the large wins are, and it's the part most setups leave switched off.

Why it matters

If you serve customers in a different country from your hosting, this is one of the cheapest speed improvements available.

Related terms

Time to First Byte (TTFB)TTFB measures how long from requesting a page until the first byte of response arrives. It captures server processing, database queries and network di…SSR, SSG and ISRThree ways of producing a web page: server-side rendering builds it per request, static site generation builds it once at deploy time, and incremental…Largest Contentful Paint (LCP)LCP measures how long until the largest visible element — usually a hero image or headline — has rendered. Google considers 2.5 seconds or less good, …

More in Web & Performance

Core Web VitalsLargest Contentful Paint (LCP)Cumulative Layout Shift (CLS)Time to First Byte (TTFB)SSR, SSG and ISRHeadless CMSProgressive EnhancementWeb ApplicationTechnical Debt

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