topic Re: UI Extension Slow Load in APIs & Integrations

UI Extension Slow Load

CHutt5 — Mon, 15 Sep 2025 15:55:11 GMT

Hi,

Has anyone had an issue with slow load on UI Extensions?

While the main HubSpot UI loads almost instantly, there is a noticeable delay when switching to the tab containing the UI extension. When the page loads in we see a loading spinner which then goes after several seconds.

We have contacted support about this and were sent a recording which didnt have this problem, so its very confusing.

Our extension includes some additional functionality—loading property values, dropdown options, and auto-populating associated objects—which can play a role in the delay. However, after testing with only the basic form (removing that extra logic), the load time seemed to remain the same.

From some investigating online, we've read it might be that HubSpot prioritizes the main UI and then loads custom extensions afterward. Is that correct? How can we fix this issue?

Thanks

Re: UI Extension Slow Load

STierney — Tue, 16 Sep 2025 01:10:54 GMT

Hey @CHutt5 - thanks for posting in the Community!

I understand that you're experiencing loading delays with UI extensions. Are you able to provide more context around the recording you were sent by HubSpot Support - specifically, what did that recording contain that negated what you're experiencing?

I'd also like to tag in some experts here who may have more context regarding this inquiry. @ChrisoKlepke, @BarryGrennan, and @HFisher7 - any thoughts for @CHutt5 here?

Shane, Community Manager

Re: UI Extension Slow Load

CHutt5 — Tue, 16 Sep 2025 11:32:57 GMT

Hi @STierney,

Thanks for you reply.

The recording showed the ui extension load in almost straight away along with the rest of the UI, whereas we face roughly 8 second delay.

There didnt seem a loading spinner in the center of the card which we are currently experiencing. From our understaning that spinner cant be controlled by ther card and is just the Hubspot UI.

Its something we need to fix quite urgently as its affecting processes.

Thanks

Cian

Re: UI Extension Slow Load

RubenBurdin — Wed, 17 Sep 2025 14:38:41 GMT

Hi @CHutt5 ,

Yes, what you’re seeing is pretty typical. HubSpot renders its own UI first and then initializes custom extensions asynchronously. That’s why even if you strip out your extra logic, the card still lags behind the main UI, HubSpot essentially queues your iframe until after the core interface is stable.

You can’t override the native spinner either; it’s HubSpot’s loader while the extension iframe gets hydrated. The official docs also point out that UI extensions are sandboxed and loaded after the main app which explains the gap.

(https://developers.hubspot.com/docs/apps/developer-platform/add-features/ui-extensibility/ui-components/overview )

What usually helps is optimizing what happens inside your extension once it loads. For instance, defer any heavy property lookups until after the initial render so the iframe can at least display a skeleton state quickly.

You can also use cached values or local state to avoid making synchronous calls before the extension is interactive. If you’re seeing 8 seconds, that’s long enough that network or API bottlenecks on the HubSpot side may be stacking with the native delay, did you test with different networks or portals to see if latency is consistent?

If keeping everything responsive across systems is the bigger blocker, platforms like Stacksync handle the real-time propagation of property values and associations outside HubSpot’s iframe cycle, so the extension doesn’t wait on fresh API calls. That way your UI loads light and the synced data follows instantly behind the scenes. Hope this helps clear up why it feels sluggish and where you can tweak.