CWV pass rate for stores with and without an email popup or form tool (HTTP Archive sample)
| Group | Pass with tool | Pass without | Median JS with | Median JS without | Stores with (CrUX) |
|---|---|---|---|---|---|
| Shopify | 61.4% | 57.3% | 3.98 MB | 2.87 MB | 5,478 |
| WooCommerce | 26.6% | 36.5% | 1.54 MB | 0.98 MB | 1,092 |
| Other store platforms | 41.3% | 41.2% | 2.08 MB | 1.39 MB | 772 |
| Top 100K stores | 44.9% | 30.9% | n/a | n/a | 285 |
| Rest of top 1M | 54.5% | 48.9% | 3.51 MB | 1.86 MB | 7,057 |
| All stores | 54.1% | 48.1% | 3.53 MB | 1.88 MB | 7,342 |
Source: PageSpeed Matters, HTTP Archive top 1M crawl and CrUX, Sept 2026. JavaScript medians not available for the Top 100K group.
Summary
Email signup forms and popups are one of the most common tools on an online store, and every one of them adds script to the page. We wanted two answers: which signup tools stores actually install, and whether stores that run one pass Core Web Vitals more or less often.
On adoption, one tool is far ahead. Klaviyo appears on 159,251 of 40.3 million homepages crawled, against 3,680 for Justuno and 1,472 for Privy. On speed, stores with a signup tool look faster at first, but most of that gap is platform mix, and on WooCommerce the pattern flips.
What we measured
We used two separate samples, and the numbers from each should be read on their own.
Adoption counts cover 40.3 million homepages crawled between January and October 2026. We counted homepages that load each vendor's scripts.
Speed figures come from the HTTP Archive crawl of the top 1M sites from September 2026, on mobile. We flagged store homepages that load a detected email popup or form tool, 7,610 stores in all, against 86,401 stores without one, and joined them to Chrome UX Report (CrUX) field data at the 75th percentile. A store passes Core Web Vitals when loading, responsiveness and visual stability are all good.
This is correlation, not cause. The speed comparisons are tool against no tool, by platform, and say nothing about any one vendor.
Klaviyo is far ahead on adoption
Across 40.3 million homepages, Klaviyo is on 159,251. Justuno is on 3,680 and Privy on 1,472. Klaviyo outnumbers Justuno and Privy combined by more than 30 to 1.
The lead likely reflects what Klaviyo is: an email and SMS platform that many stores already use for their campaigns, with signup forms included. A store that sends email through it can add forms without installing a separate popup tool.
Stores with a signup tool pass more often overall
Top 1M stores running an email popup or form tool pass Core Web Vitals 54.1% of the time (7,342 with CrUX data), against 48.1% of stores without one (78,945). They do this while carrying a median 3.53 MB of JavaScript, against 1.88 MB.
That gap is mostly about platform. 73.5% of the 7,610 stores with a detected popup or form tool run on Shopify. Shopify stores pass Core Web Vitals more often than stores on most other platforms, so a group that is mostly Shopify will look faster whatever tools it carries. Signup tools do not make stores faster.
Platform by platform, the gap shrinks or flips
Comparing stores on the same platform removes most of the platform effect. On Shopify, stores with a popup or form tool pass 61.4% of the time (5,478 with CrUX data) against 57.3% without (39,779). They still carry more script: a median 3.98 MB of JavaScript against 2.87 MB.
On WooCommerce the pattern flips. Stores with a popup or form tool pass 26.6% of the time (1,092 with CrUX data) against 36.5% without (19,450), with a median 1.54 MB of JavaScript against 0.98 MB.
On other store platforms there is no difference: 41.3% pass with a tool (772) against 41.2% without (19,716).
Top 100K stores show the widest gap
Among the most visited stores, the ones in the Top 100K, stores with a popup or form tool pass 44.9% of the time (285 with CrUX data) against 30.9% without (3,441). The rest of the top 1M shows a smaller gap: 54.5% with a tool against 48.9% without.
The Top 100K group with a tool is small, so treat that result with care. Larger stores also tend to differ in platform, budget and engineering time, any of which could sit behind the gap.
What this means for your store
A signup form can be worth the script it adds, but on most platforms other than Shopify, stores with one pass Core Web Vitals no more often, and on WooCommerce less often. How the tool is loaded matters more than which one you pick.
- Load the form script after the main content renders, not in the page head.
- Show popups after a delay or a scroll rather than on load, so they do not compete with the main image.
- Reserve space for embedded forms so they do not shift the layout when they appear.
- Remove old form or popup scripts when you switch tools, so the page is not loading two.
Then test your homepage and a product page in PageSpeed Insights before and after, so you can weigh the speed cost against signups.
Sources
- PageSpeed Matters analysis of 40.3M homepages crawled January to October 2026
- HTTP Archive crawl of the top 1M sites, September 2026, mobile
- Chrome UX Report (CrUX) documentation, Google: https://developer.chrome.com/docs/crux
Embed this research
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<script>window.addEventListener("message",function(e){if(e&&e.data&&e.data.psmEmbed==="email-signup-tools"&&e.data.height){var f=document.getElementById("psm-email-signup-tools");if(f){f.style.height=e.data.height+"px";}}});</script>
<p style="font:14px/1.5 system-ui,sans-serif">Source: <a href="https://www.pagespeedmatters.com/resources/data-studies/email-signup-tools">Email Signup Tools: Klaviyo Outnumbers Justuno and Privy 30 to 1 - PageSpeed Matters</a></p>
Frequently asked questions
What is the most popular email signup tool for online stores?
Klaviyo, by a wide margin. Across 40.3 million homepages crawled since January 1, 2026, it appears on 159,251, against 3,680 for Justuno and 1,472 for Privy.
Do email popups slow down a store?
It depends on the platform. On Shopify, stores with a popup or form tool pass Core Web Vitals 61.4% of the time against 57.3% without. On WooCommerce they pass 26.6% against 36.5%, and on other store platforms 41.3% against 41.2%.
Why do stores with signup tools pass Core Web Vitals more often overall?
Platform mix. 73.5% of the 7,610 stores with a detected popup or form tool run on Shopify, and Shopify stores pass more often in general. Compared platform by platform, the gap shrinks, disappears or flips.
How much JavaScript do stores with a signup tool load?
In the top 1M, stores with an email popup or form tool load a median 3.53 MB of JavaScript, against 1.88 MB for stores without one. On Shopify the medians are 3.98 MB against 2.87 MB.
Signup forms can grow your list without slowing the page, as long as their scripts load after the content shoppers came for. Need help with this? See our conversion rate optimization agency.