Will Microsoft Clarity Slow Down My Website?

The official party line is no. But end users sometimes say otherwise. Here are both sides of the story, and how to tell if installing MS Clarity is likely to impact your website performance—specifically page load time.

Why Microsoft is right

Microsoft says Clarity is asynchronous and that most users see no measurable impact on page load time. In fact, they’ve said this many times over the years:

Because Clarity’s script is designed to load asynchronously, it shouldn’t block the browser from rendering the page in the way a synchronous script can. This is the core reason for Microsoft’s claim that most users won’t notice a speed change.

Why webmasters are right

There are a lot of independent reports from site owners who do see slowdowns in page speed, especially when Clarity is combined with other third-party scripts or the site is already script-heavy.

Any extra JavaScript still adds network requests, parsing, and execution work, so a small performance cost can still happen in real-world conditions.

Sites with a lot of tags, ads, pixels, or heavy JavaScript are more likely to notice the difference because all those scripts compete for the same browser resources.

<div class="post-note">Some of these claims come from UGC in forums like Reddit, Github, and Stack Overflow. I’d trust those generally because they come from people trying to figure out problems together. Other claims come from sites like this one where they’re selling a solution. That last example is still a helpful article overall, and of course there’s astroturfing on Reddit. Always consider the source.</div>

Bottom line: It depends

So, will installing MS Clarity slow down <em>your</em> website? The actual effect depends on your page structure, tag manager setup, and other third-party code.

Clarity usually has little to no noticeable effect on website performance. But it can still slow down a website under the wrong conditions.

What you should do is test before and after installing MS Clarity, using Core Web Vitals or lab tools like Lighthouse.

If Clarity shows up in your measurements, you can usually reduce the impact by:

Limiting where it loads
Deferring noncritical scripts
Trimming other third-party tags

You can also install MS Clarity for a set amount of time to gather the insights you want, and then uninstall it. Systematic “spot checks” can help you gather the type of data you’re looking for without having it running constantly.

I think Microsoft Clarity is a great tool, but that’s not what this blog is about. It’s about answering a question we frequently hear from our clients so you can better understand the potential website performance impact, and how to spot/mitigate it if need be.

FAQ

What’s a script, and what does asynchronous mean?

A script is a piece of code that tells your website to do something. That “something” could be tracking user behavior, loading a chat widget, firing an ad pixel, or running a tool like Microsoft Clarity.

“Asynchronous” means the script can load in the background instead of forcing the page to wait for it before showing the content. That’s why Microsoft says Clarity usually doesn’t have a noticeable effect on page speed.

But asynchronous doesn’t mean “free.” The browser still has to download the script, read it, and run it. So while async scripts are less likely to block the page, they can still add some performance cost, especially on pages that already have a lot going on.

How can I tell if my website is “heavy” and likely to be slowed down by Clarity?

Your site is more likely to feel the impact if there’s already a lot of third-party stuff on it: ads, pixels, cookie tools, chat widgets, A/B testing tools, or a lot going on in tag manager. When there’s lots of code fighting for attention, adding one more script to the pile can be more noticeable.

If you suspect this might be the case for your website, run Lighthouse or check Core Web Vitals before installing Clarity, then test again after. If Clarity shows up in the waterfall or third-party code impact, your site probably doesn’t have much tolerance for additional scripts.

What’s the best way to test whether Clarity is hurting page speed?

Test the page before and after installation using the same template, device conditions, and tools. Check Lighthouse for lab data, and check Core Web Vitals or other real-user metrics to learn what actual visitors experience. As always, you want to look for a pattern, not one point-in-time score.

<div class="post-note-cute">If you’re trying to figure out whether Clarity is worth installing, or whether it’s actually affecting your page speed, we do this kind of troubleshooting all the time. <a href="https://momenticmarketing.com/contact">Feel free to reach out</a> if you want a second set of eyes.</div>