CDN Usage Test

What is it?

A Content Delivery Network (CDN) is a globally distributed system of servers that caches and serves your static assets, images, JavaScript, CSS, fonts, from edge locations close to each visitor. Routing assets through a CDN reduces latency, improves cache hit rates, and offloads traffic from your origin server, producing faster, more consistent page performance for visitors worldwide.

Why CDN usage still matters in 2026

The speed of light is a fixed constraint, and a single origin server in one region simply cannot serve users on the other side of the planet quickly. A CDN solves this by replicating your assets to dozens or hundreds of edge locations, so a visitor in Tokyo retrieves your hero image from Tokyo, not from Virginia. The latency reduction is often the single largest performance win available, especially on global sites.

Modern CDNs also bundle features that would be expensive to implement on your own origin: automatic image format negotiation (serving WebP or AVIF when the browser supports it), edge-level compression, intelligent caching, DDoS protection, and edge-side rendering of personalized HTML. Even free CDN tiers from providers like Cloudflare offer most of these capabilities, making CDN adoption one of the highest-impact, lowest-cost upgrades available to most sites.

Common CDN gaps this test catches

No CDN at all, with assets served directly from a single origin server.
CDN configured but bypassed for some assets, often where image or font URLs still point at the origin hostname.
Cache headers preventing caching, which forces the CDN to revalidate every request and defeats much of the benefit.
Origin-only third-party scripts: many vendors already serve their scripts via their own CDN, but stale embeds may still hit the vendor's origin.

This test detects whether your static assets are served through a CDN and which ones may be bypassing it. The fix guide below covers signing up for a CDN, configuring it correctly, ensuring assets are routed through it, and setting cache headers that let the CDN do its job.

Pass rate:

Top 100 websites: 95%
This value indicates the percent of top 100 most visited websites in the US that pass this test (in the past 12 months).
All websites: 37%
This value indicates the percent of all websites analyzed in SEO Site Checkup (500,000+) in the past 12 months.

Pass rates of Top 100 US websites
2021	96%
2022	96%
2023	97%
2024	95%

100

How do I fix it?

A Content Delivery Network serves static assets from edge locations close to the user, reducing latency, improving cache hit rates, and offloading traffic from the origin server. Fixing this issue means routing your images, JavaScript, CSS, and fonts through a CDN so visitors anywhere in the world get fast, consistent delivery.

Where to make the change

Cloud platforms: Cloudflare, Fastly, AWS CloudFront, Bunny.net, and similar providers offer free or low-cost CDN tiers. Sign up, point your domain through the CDN, and enable caching for static asset paths.
WordPress: use a CDN integration plugin or sign up directly with Cloudflare and update the site's nameservers.
Shopify: Shopify serves storefront assets through its own CDN automatically; the failure usually points at custom assets uploaded outside the platform.
Headless or framework sites: deploying to Vercel, Netlify, or Cloudflare Pages puts the entire site behind a global CDN by default.

Common causes and how to resolve them

No CDN at all: add one. Even a free Cloudflare account in front of an existing host produces measurable speed gains.
CDN configured but bypassed for some assets: ensure all img, script, link, and font URLs use the CDN hostname rather than the origin.
Cache headers prevent caching: long-lived assets need cache-control headers like public, max-age=31536000, immutable. Without them, the CDN cannot cache effectively.
Origin-only third-party scripts: many vendors already serve their scripts via their own CDN. Use the URL the vendor provides rather than self-hosting.

Best practices

Use a versioned asset path: filenames like app.a3f9.css let you set far-future cache headers without ever serving stale files. Update the filename when content changes.
Enable Brotli at the edge: most CDNs can compress responses on the fly, including text formats.
Pre-warm caches for new launches: after a major release, request key URLs through every region (or use the CDN's purge-and-prefetch tools) so users do not hit cold caches.