Does Klaviyo slow down your Shopify store?

Someone opens the link to your candle

Does Klaviyo slow down your Shopify store? It can, for the first few seconds on a product page, and those are the seconds when a shopper decides whether to stay.

Picture one person opening the link to your candle on their phone. You added Klaviyo so you can still reach them after they leave, with a welcome offer when they sign up or, if they are already on your list, a reminder about that candle later on.

For either email to happen, Klaviyo has to be on the candle page with them while they are still looking. That is the part that can get in the way, and it is also the part you want to keep.

What Klaviyo puts on the candle page

So what is Klaviyo doing on that page? It runs a small program that the phone downloads from Klaviyo’s own website, a file called klaviyo.js. Klaviyo’s help page says that on Shopify you do not paste it in yourself, because the Klaviyo switch in your theme settings adds it, and Shopify calls that switch an app embed.

The program has two jobs on the candle page. It notes that this person looked at this candle, which Klaviyo calls Viewed Product, and Klaviyo’s Shopify setup page says that note is what a reminder email is built from. The same page says the signup forms only work once this is switched on, so the program is also what shows the popup.

Meanwhile, the phone has its own list for that page. It has to fetch the layout, the candle photo, the price and the Add to cart button, and it can only do so much at once. Shopify’s performance guide says the browser has one main lane for drawing the page and running programs, and every app’s program competes for time in it.

So when klaviyo.js gets in first, the candle photo waits behind it. The shopper is looking at an empty box where the candle should be, while a program for a later email is starting up. That is the slowdown people mean when they ask about Klaviyo.

People who build websites call a program like this a third-party script, which only means code that comes from another company’s website rather than from your store.

Why you keep Klaviyo and let it wait

The photo is how you sell the candle today. Klaviyo’s program is how you get a second go at it later. You need both, and they do not need to start at the same moment.

Think about what the popup is asking for. Nobody signs up for news about a candle they have not seen yet, so the form does its job better a few seconds in, once the photo is up and they have had a look. The Viewed Product note still gets made, as long as the program starts before they leave.

I know what some of you are thinking. Why not uninstall Klaviyo and be done with it? Because that also takes away the welcome email and the reminder, which are the reason you installed it. The photo can show up first either way, and only one of those ways keeps the emails.

There are two things you can leave alone. Pausing a campaign or a flow changes what lands in inboxes, not what the candle page downloads. Telling the popup to appear only on your homepage may not help either, because Shopify’s guide notes that email popups often load on every page even when they are set to show on only some.

What still has to be right is the order. The candle photo first, then Klaviyo’s program, then the popup.

Check your product page, then change the order

Let’s start with what the shopper sees. Open one of your product pages on your phone from a normal link, the way a customer would, rather than from the theme editor. Watch the first few seconds, and notice which arrives first, the photo or the popup, and whether the photo sits blank for a moment.

Next up, the list of files. On a computer, open the same page in Chrome, right-click anywhere and choose Inspect, which opens a panel beside the page. Click the Network tab, which lists every file the page downloads, tick Disable cache so you see what a first visit gets, and reload.

Type klaviyo in the filter box at the top of that list, and you will see klaviyo.js and a few other files from static.klaviyo.com. Clear the filter, click Img so the list shows only pictures, and find the candle photo. If Klaviyo’s files start well before the photo and the photo arrives late, the photo is waiting in line behind them.

There are two ways to change that order. Shopify’s guide shows how to start a program like this only after the shopper scrolls, which is a small edit to the theme, and it is a good option if someone already looks after your code.

If you would rather not edit the theme, this is the one job Whoosh does here. Smart App Loading holds programs like klaviyo.js until the product photo is on screen, without copying your theme or uninstalling Klaviyo, and its built-in 50/50 test shows on your own store whether more people buy.

Smart App Loading is US$99 a month with a 7-day free trial. TileCloud’s published case study with Whoosh shows a 10% conversion lift.

If you already have a speed app, check which wait it moves before you add another one. The guide to speed apps sorts the listings by the wait each one fixes, and a popup finishing before the product is one of those waits.

Whichever way you go, test Klaviyo afterwards. Klaviyo’s setup page gives the check: add ?utm_email=you@example.com to the end of your homepage address with your own email, reload, open the candle page, then search for your email in Klaviyo and look for Viewed Product on your profile.

Then do what a new shopper would. Open the popup on your phone, sign up with a spare address, and wait for the welcome email to arrive.

Now, when can you stop? Google measures this moment as Largest Contentful Paint, the time until the biggest thing on the screen appears, which on a product page is usually the photo. Google’s page on it wants that within 2.5 seconds, and the Core Web Vitals report in Search Console shows whether your real visitors get there.

You are done when most real visits see the photo in time, or when the file in front of the photo is no longer Klaviyo’s. If it is your reviews or chat app instead, the same fix applies. If the photo itself is the slow download, that is a different check on the photo file, and our speed check shows you which of the two you have.