Short answer: A CDN, or content delivery network, keeps copies of your site’s files on servers in many places, so each visitor gets them from one nearby. It helps most when your visitors are far from your server; for a local business with a fast server, measure before you add one.
How a CDN works
MDN describes a CDN as a group of servers spread out over many locations that store copies of data, so the server closest to each user can answer. Your own server, which the CDN copies from, is what web.dev calls the origin.
web.dev explains that CDN servers sit closer to users than the origin, so the round trip is shorter. Their caches also spare many requests the trip to the origin.
Files that rarely change, such as images, videos and versioned scripts, should be cached with a long lifetime: web.dev gives 6 months or 1 year as examples. Pages can be cached too, if the CDN can purge them quickly when they change.
What a CDN can and can’t do
| What a CDN brings | What it means | What to check |
|---|---|---|
| Shorter distance | Servers closer to your visitors cut the round trip | Where your visitors actually are |
| Less load on your server | Stored copies answer most requests and absorb traffic spikes | How much the CDN serves from its cache |
| Faster connections | Many CDNs offer Brotli, TLS 1.3 and newer HTTP versions | That each feature is switched on |
| One more dependency | If the CDN goes down or is blocked, your site can fail | What happens when it is unavailable |
| A possible slowdown | MDN warns a CDN can also make a site slower | Your own pages, with and without it |
From web.dev’s guide to content delivery networks and MDN’s CDN entry, read November 4, 2026.
web.dev adds that because CDNs reduce server load, they cut server costs and suit traffic spikes. MDN adds the other side: a CDN is one more service your site depends on, and one more place an attacker could target.
How to decide on a CDN and set it up
- Find out where your visitors are, in your analytics.
- Measure the first byte and LCP of your main pages for those visitors.
- Pick a CDN and point your domain, or only your static files, to it.
- Cache versioned files for a long time, and keep pages short or purge them when you publish.
- Switch on Brotli, TLS 1.3 and HTTP/2 or HTTP/3 if the CDN offers them.
- Make logged-in visits and personal pages skip the CDN’s cache.
- Measure again with and without the CDN before you keep it.
Our TTFB guide covers the first byte, and our website caching guide covers what never belongs in a shared cache. Our HTTP/2 and HTTP/3 guide shows how to check the protocol.
What we found when we tried one
On October 8, 2026, we put Cloudflare’s network in front of our site. Then we ran Lighthouse on our home page in English and Spanish, alternating between our server directly and the CDN.
On a slow mobile connection, the main content appeared sooner straight from our server: 2.96 seconds against 3.16 in English, and 1.86 against 2.49 in Spanish. On the simulated phone the median score was 93 for both. On desktop the CDN won, 0.71 seconds against 0.81.
It didn’t win everywhere, so we took it out the same day. Our own page cache already answers in about 40 milliseconds. As of November 4, 2026, our site answers straight from our server, with no CDN in front.
Before you keep a CDN
- You know where your visitors come from.
- Your pages load faster with the CDN in your own tests.
- Versioned files are cached for a long time.
- Pages are purged when you publish.
- Personal pages skip the CDN’s cache.
- You know what happens if the CDN is down.
RememberA CDN shortens the distance to your visitors. If your server is already close and fast, test before you pay for it.
Server and delivery settings like these are part of our technical SEO service.
Quick answers about CDNs
What is a CDN?
A content delivery network: a group of servers in many places that keep copies of a site’s files, so the server closest to each visitor can answer. Your own server, the origin, still holds the original.
Does a CDN make a website faster?
Often, for visitors far from your server, because the copy travels a shorter way. MDN warns it can also make a site slower, so measure your own pages with and without it before you keep it.
Is a CDN the same as web hosting?
No. Hosting runs the origin server that builds your pages. A CDN sits between that server and your visitors and serves copies of what it can store.
What should a CDN cache?
Static files such as images, videos and versioned scripts and stylesheets, with a long lifetime: web.dev gives 6 months or 1 year as examples. Pages can be cached too if the CDN can purge them quickly when they change.
What are the risks of using a CDN?
MDN names two: an extra service your site depends on, which can break it if it goes down or is blocked, and an extra point an attacker could use to serve bad files.
Sources
Read on November 4, 2026. web.dev: Content delivery networks (CDNs) and Optimize Time to First Byte. MDN: CDN. Our case: Lighthouse on our home page with and without a CDN on October 8, 2026, and how our site answers on November 4, 2026.