Do Review Apps Slow Down Your Store?

Short answer: Some review apps do measurably slow a Shopify store down, but the cause is almost always one of four specific things — a webfont downloaded just for star icons, an iframe loading a second page inside yours, a script that blocks the page from rendering, or one separate widget instance per product card on a collection page — not "review apps" as a category.

Why would a reviews widget slow anything down?

A webfont downloaded for the star icons. Some widgets ship their own icon font just to draw five stars, which means your visitor's browser fetches a whole font file before it can show a rating that could have been five characters of Unicode or a tiny inline SVG.

An iframe loading a second page inside yours. An iframe is a browser tab within your page — it has to load, parse and render its own document, with its own network requests, on top of everything your storefront is already doing.

A script that blocks the page from rendering. A script placed without async or defer, or one that runs before the rest of the page paints, holds up everything below it — the browser waits on it even if the reviews themselves are three sections down.

One widget instance per product card on a collection page. A collection page can show dozens of products. A widget built for a single product page, then reused once per card, multiplies every one of the problems above by the number of products on screen.

How to measure it yourself

Open your storefront in Chrome, right-click and choose Inspect, then open the Network tab and reload the page with the cache cleared. Do this once before installing a review app and once after, on the same product and collection pages, and compare total requests and total page weight.

Chrome's own Lighthouse panel, or PageSpeed Insights run against your live URL, gives you a score and a waterfall — look specifically for anything the report attributes to the app's script or domain.

The comparison only means something if you test the same page both times. A busy product page with fifteen images will always be heavier than a plain one; what you're isolating is the difference the app itself adds.

What a fair size looks like

There's no single right number, but a script that adds tens of kilobytes gzipped, loads without blocking the page, and renders inside its own contained element rather than an iframe is a reasonable bar for a reviews widget.

Kudo's storefront widget is 34 KB gzipped, downloads no webfont, and renders inside a shadow root — a contained element the host page's CSS can't reach into, and that can't reach out into the host page either. It reads reviews from a public, read-only endpoint, so nothing in the page itself carries a database key.

That's one data point, not a universal standard — use it as a reference when a vendor's answer to "how big is your script" is vague.

Five questions to ask before installing a review app

Does it load a webfont, or does it draw stars without one? A webfont for five star icons is weight a font already on the visitor's device could have skipped.

Does it render inline, or inside an iframe? An iframe is a second page loading inside yours; inline widgets with their own contained styling avoid that cost.

Does the script block the page, or load without holding it up? Ask specifically whether the tag is marked to load asynchronously.

On a collection page, is it one request for the whole grid, or one per product card? This is the multiplier that turns a small script into a real slowdown.

Can they tell you the gzipped size? A vendor who can answer this in one sentence has almost certainly measured it; a vague answer is itself information.

Where this connects to your collection pages

The heaviest version of this problem shows up on the collection grid specifically, where a widget built for one product gets asked to run once per card — that's the case worth checking first if a slowdown appeared right after installing reviews. Beyond size, here's what else to look for when you're comparing review apps, including the parts that are harder to measure than kilobytes.

The Two-Minute Version

Kudo's widget is 34 KB gzipped, skips the webfont, and renders inside a shadow root instead of an iframe — that's what "a fair size" above is describing.

Start free at getkudo.co.

Frequently Asked Questions

Do all review apps slow down Shopify stores?
No. The slowdown comes from specific implementation choices — a webfont, an iframe, a blocking script, or per-card widgets on a collection page — not from showing reviews itself.

What's a normal size for a reviews widget script?
There's no official number, but tens of kilobytes gzipped, loading without blocking the page, is a reasonable bar. Ask the vendor directly if their site doesn't say.

Does Shopify's own speed score catch this?
Lighthouse and PageSpeed Insights will show the added weight and any render-blocking script, but they score the whole page — a small app can still be the biggest single item on the waterfall even if the overall score looks fine.

Is an iframe always bad?
Not always, but it always costs more than inline rendering — a second document has to load and render on top of your page's own. If a vendor uses one, ask why.

Can I test this before I install anything?
Most apps offer a free tier or trial. Install it on a development theme first, run the before-and-after Network tab comparison, and decide before it's live on your real storefront.