If a product page feels slow when the customizer loads, this guide explains why and what to check. It is written for merchants who want to understand where the time goes and rule out a stuck customizer. Most of the time a slow first load is your network or your theme, not Composerie.
How the customizer is built to stay fast
Composerie is designed to add as little weight to your store as possible. How much it adds depends on the storefront mode of the product.
Products in Linked mode load nothing at all. No JavaScript, no network requests, no extra markup on the page. The design is resolved on our side when the order comes in, so the product page carries no Composerie weight. If most of your catalog uses Linked mode, those pages are unaffected.
Products in a visible mode (Full Upper PDP or Full Page) load a small script with the defer attribute. Deferred scripts do not block the rest of the page from rendering. The heavy editor runtime is loaded separately, and only for the mode that is actually in use. So the page can paint and become usable while the customizer finishes loading.
When the customizer needs your variant mapping, it requests it once. If several parts of the page ask for the same mapping at the same time, they share a single request instead of firing one each. The result is then cached in your browser for 60 seconds. Reload the page in the same visit and the customizer reads from that cache instead of calling the API again. On top of that, the mapping response is cached at the CDN for five minutes, so visitors who hit a warm cache get an instant answer.
There is also a hard limit so the page can never freeze on us. The mapping request is given 5 seconds. If it takes longer, it is cancelled and fails fast rather than hanging the page. So a true, lasting hang is almost never a stuck Composerie request. It points at something else on the page.
What to check when a page feels slow
Work through these checks in order. They separate a slow connection or a heavy theme from an actual customizer problem.
Hard refresh the page once
Do a hard refresh to clear a stale cache and force fresh files. On Windows press Ctrl plus Shift plus R. On a Mac press Cmd plus Shift plus R. If the page is fast on the second, normal load, the first load was just warming the cache and the session is now primed.
Test on a different network or device
Open the same product page on another connection, for example mobile data instead of wifi, or on a different device. If it is fast elsewhere, the slow load was the connection, not the customizer.
Check for other apps or a heavy theme
Other storefront apps, large hero images, and heavy theme scripts all compete for the same page load. To test this, duplicate your theme, switch the copy to a clean default theme, and load a customizable product on it. If the page is fast on the default theme, the slowdown is coming from your live theme or another app, not Composerie. See theme compatibility and supported themes for what we test against.
If the customizer never appears, treat it as a load failure
A page that is merely slow will still show the customizer once it finishes. A page where the customizer never shows up is a different problem. Follow the customizer not appearing guide instead of this one.
Frequently asked questions
Does Composerie slow down all my product pages?
No. Products in Linked mode load no Composerie code and make no requests on the storefront. Only products in a visible mode load a small deferred script, and that does not block the rest of the page.
The customizer takes a while to appear on the first visit. Is that normal?
Yes. The first visit loads the bundle and the variant mapping once. Both are cached for the rest of the session, so reloads in the same visit are quick.
The page seems to hang on the customizer. What is happening?
It is most likely not Composerie. The mapping request is cancelled after 5 seconds and fails fast, so it cannot freeze the page. A lasting hang usually points at the theme or another app. Test the page on a clean default theme to confirm.
I changed a setting but the storefront still looks the same.
That can be a caching effect rather than a speed problem. The mapping is cached in your browser for the session and at the CDN for a few minutes. See the changes not showing guide for how to force a refresh.
If none of these checks resolve the slowdown, gather the product URL and the browser you tested with, then contact support.
Next: if a setting you changed has not shown up yet, read changes not showing.