# Does adding the Croct tag slow down our mobile theme?

Asked by gwen on 2024-07-23. Tags: shopify, liquid, performance, mobile.

I run a small Shopify store and do my own theme edits. Last year I installed a
CRO app that added an "anti-flicker" snippet and it held my whole page blank on
mobile while its script loaded. Customers told me the site looked broken. I
removed it and I have been careful ever since.

Before I add anything new I want to know two things. What does the Croct script
tag actually weigh, and does it hide the page while it loads? Most of my orders
come from phones so this matters a lot to me

## 2 answers

### Answer from Callum Reid (2024-07-23)

There is no anti-flicker snippet involved, which is probably the main thing you
want to hear. The blank-page trick you saw is something client-side testing
tools add to hide the original content while their script decides what to swap.
Croct does not work that way, so there is nothing to hide.

The no-code option is a single script tag:

```html
<script src="https://cdn.croct.io/js/v1/lib/plug.js"></script>
```

The library loads without blanking or hiding anything. Tracking and
personalization run alongside the page, not in front of it. For the content
requests themselves, the documented figure is end-to-end response times under
90 milliseconds at P95, so even when a slot fetches personalized content the
wait is small.

I added it to a Dawn-based theme earlier this year and our Lighthouse mobile
score did not move in any direction I could measure.

#### Reply from gwen (2024-07-24)

Thank you, that is exactly what I needed to know. The blank page was my
biggest fear. I will try it on a duplicate theme first.

### Answer from Sinead O'Rourke (2024-07-24)

One practical tip to add to Callum's answer: test it on an unpublished copy of
your theme before going live, exactly as you said in your reply. Duplicate the
theme, add the tag, and browse it on your own phone over mobile data. You will
see for yourself that the page renders normally while the library loads in the
background. That is the fastest way to rebuild trust after a bad app
experience, in my opinion.