Microsoft Clarity: impact on page speed
Category: Session recording and heatmaps
Microsoft Clarity records sessions and heatmaps free of charge. Like other recording tools it observes the page continuously while a visitor is on it.
On 8.2 % of the 4108 homepages measured, Microsoft Clarity is among the five heaviest third parties. Where it is, it takes a median of 85 ms of main-thread time; on the heaviest quarter of those sites it takes 136 ms or more.
8.2 %
of homepages: among the five heaviest third parties
85 ms
median main-thread time
136 ms
main-thread time on the heaviest quarter (p75)
28 KB
median transfer size
Distribution across homepages
Percentiles across 335 homepages with Microsoft Clarity.
| Percentile | Main-thread time | Transfer size |
|---|---|---|
| p25 |
69 ms
|
28 KB |
| Median |
85 ms
|
28 KB |
| p75 |
136 ms
|
29 KB |
| p90 |
239 ms
|
29 KB |
In context
By median main-thread time, Microsoft Clarity ranks 35th of 65 third parties in the benchmark, lighter than Hubspot and heavier than Cookiebot.
On 9.3 % of the homepages where it appears, Microsoft Clarity alone uses 250 milliseconds of main-thread time or more, the mark from which Lighthouse flags third-party code.
Homepages with Microsoft Clarity weigh 5.4 MB at the median (JavaScript: 1.9 MB), homepages without it 4.2 MB (JavaScript: 1.6 MB).
Often loaded together with
Share of homepages with Microsoft Clarity where the other tool is also among the five heaviest third parties.
- Google Tag Manager 86 %
- Facebook 50 %
- TikTok 17 %
How to spot Microsoft Clarity on your page
Clarity loads a small tag from www.clarity.ms and its recorder clarity.js from scripts.clarity.ms, then uploads recording data in batches to a collect endpoint on clarity.ms; Lighthouse lists the tool as "Clarity". Because it is free, it is often installed in addition to another recording tool, so two recorders observe the same page. If both appear in your third-party list, keep the one your team actually uses.
How to reduce the impact of Microsoft Clarity
- Enable Clarity for analysis periods rather than permanently.
- Exclude pages that do not need behavioural analysis, such as legal pages or account areas.
- Load the script only after consent.
Frequently asked questions
How can I load Microsoft Clarity with less impact?
Enable Clarity for analysis periods rather than permanently. Exclude pages that do not need behavioural analysis, such as legal pages or account areas.
Does Microsoft Clarity affect Core Web Vitals?
Microsoft Clarity works like other session recorders: it captures the structure of the page and tracks interactions throughout the visit. The cost lands on the main thread and shows in INP, particularly on long pages with many DOM changes such as product lists or infinite scroll. Clarity has no visible widget, so it does not cause layout shifts.
Method and sample: Third-Party Benchmark.