Can you add personalisation without paying the speed tax?
Merchants veto apps on speed before they get to features. Two of them, in the same week, independently called it the speed tax and the performance tax. If you are evaluating personalisation, this is the question to settle first.
- Every app has two costs: the monthly fee and the script weight.
- The fee stops when you uninstall. Leftover theme code often does not.
- An app block you place yourself beats an app that edits theme files.
- Consolidating is not automatically faster. One big app can load more JavaScript than three focused ones.
“Every app is two costs: the monthly fee and a performance tax.”
“Every app has two invoices: the monthly fee, and the speed tax.”
“the subscription cost disappears immediately but the speed cost often does not”
“Any app that edited my theme files instead of using an app block.” — asked what they most regretted installing
“If an app only matters on product pages, don’t let it run sitewide.”
Separate posters, Shopify Community, August 2026. The first two coined the same metaphor a day apart, which is a good sign it is how the category actually thinks.
- 1Record your Web Vitals on a product page and the cart, before installing anything.
- 2Install one app. Change nothing else.
- 3Re-record the same two pages, same device class, same connection.
- 4Check what loads where. If it only matters on product pages, it should not run sitewide.
- 5Uninstall, then check the theme for leftover snippets. This is the step people skip.
One Shopify Partner makes the point that gets missed: a consolidated app can ship more JavaScript than several focused ones. Measure before assuming that fewer apps means faster.
The prompt is an app block. You place it where you want it, and removing the block removes the prompt. Nothing is written into your theme layout.
The recommendations are served from your own domain through the app proxy rather than from a third-party script injected sitewide. You can add it to an unpublished theme and walk the whole flow before any shopper sees it.
We would rather you measured this yourself than took the paragraph above on trust. Steps one to five, above.
Does the prompt load for every visitor?
It loads where you place the block. A shopper who does not open it does not pull the rest of the flow.
What happens to the block if we uninstall?
Removing the app removes the block. The recommendation detail already written onto your products stays, because that is your data on your products.
Can we preview before publishing?
Yes. Add it to an unpublished theme and walk the full flow with your own tracker first.
Is there a measurement we should watch after install?
Largest Contentful Paint and total blocking time on the pages carrying the block, against the same pages before install.