Understanding Cloudflare Speculation Rules: How They Make Your Website Load Faster

When you open your browser's DevTools and see a mysterious request like /cdn-cgi/speculation, you might wonder — what on earth is that? If you're using Cloudflare, it's not a bug or a random file someone snuck in. That little request is part of Cloudflare's Speculation Rules — a smart, behind-the-scenes optimization system that quietly makes your website feel faster and smoother to visitors.

Let's talk about what it does, why it exists, and whether you should keep it on (spoiler: yes, you should).

What Are Cloudflare Speculation Rules?

Speculation Rules are Cloudflare's implementation of a relatively new browser technology called the Speculation Rules API, developed by Chrome and other modern browsers. The concept is simple: your website can predict what page a user is likely to click next and start preparing that page in the background — before they even click it.

Think of it like your website saying:

"Looks like you're reading my homepage — chances are, you'll click the About Us or Contact link next. Let me quietly get those ready for you."
by Author

When that prediction is right (and it often is), the next page loads almost instantly. No DNS lookup delay. No TLS handshake pause. No waiting for HTML to download.

It's all pre-warmed and ready.

How It Works Under the Hood

When your site is behind Cloudflare, the platform automatically injects a small JSON file at this endpoint:

https://yourdomain.com/cdn-cgi/speculation

This file defines speculation rules — a set of prefetching or preconnecting instructions that modern browsers can interpret.

Example (simplified):

{
"prefetch": [
{ "source": "document", "urls": ["/about-us", "/contact", "/services"] }
]
}

Here's what happens next:

The browser sees those rules.

It starts quietly opening network connections (TCP + TLS) or downloading small portions of those pages in the background.

When the user actually clicks one of those links, the browser already has most of the work done.

The result? A nearly instant navigation experience.

Why It Sometimes Appears "Slow" in DevTools

If you open your Network tab, you might see the /cdn-cgi/speculation request taking a long time — sometimes several seconds, or even minutes. Don't panic. It's not actually slowing your website. Here's why:

The speculation request runs after your main page finishes loading.

It's low priority and non-blocking — browsers treat it as background work.

Sometimes, Cloudflare's backend or network nodes delay the response slightly, but users won't notice because it doesn't affect rendering.

In short, even if you see a "2-minute load" in DevTools, that's just Chrome being patient — your visitors aren't waiting that long.

Why You Should Keep It Enabled

Keeping Cloudflare's Speculation Rules enabled is a smart move for most sites.
Here's what you gain:

Faster page-to-page navigation - Visitors clicking between pages will notice smoother transitions. It feels like your website is "reading their mind."
Better Core Web Vitals - Metrics like Interaction to Next Paint (INP) and First Input Delay (FID) benefit because the next page starts loading sooner.
Automatic optimization - You don't need to write a single line of code. Cloudflare automatically manages the rules, adjusts them, and ensures they only apply where safe.
Works great with modern browsers - All major Chromium-based browsers (Chrome, Edge, Brave, etc.) already support speculation rules. Safari and Firefox are also experimenting with it.

When You Might Disable It

Speculation Rules are safe for public-facing sites, but in a few rare cases, you might want to turn them off:

You run personalized dashboards or admin panels where prefetching private data isn't ideal.

You're debugging network requests and want deterministic, no-prefetch behavior.

You operate in low-bandwidth environments where every background request counts.

Otherwise, leave it on — Cloudflare knows what it's doing here.

The Bigger Picture: Predictive Web Browsing

This feature is part of a bigger shift in how browsers handle performance. For years, developers manually used <link rel="prefetch"> and <link rel="preconnect"> tags to optimize loading. Now, Cloudflare automates that logic dynamically — powered by real-world usage data, link patterns, and behavior prediction. Essentially, your website starts to act like a smart app — anticipating the next step before your visitor even takes it.

Final Thoughts

That mysterious /cdn-cgi/speculation request you saw in DevTools isn't a problem — it's a quiet performance booster. It's Cloudflare's way of making your site snappier, without you lifting a finger. So the next time you notice it hanging in the network panel, smile — that's your CDN warming up for your next visitor.

Fast pages, happy users, better SEO. You don't need to tweak anything. Just let Cloudflare speculate.