Performance issue with large collections: UI freezes with thousands of requests

[zhangqxgz]

Description

When a Bruno project contains thousands of requests (APIs), the application becomes extremely sluggish and UI freezes occur. Opening the application or expanding folders causes severe performance degradation.

However, if the requests are split into multiple separate Bruno projects (by adding \�runo.json\ to subfolders), the performance is normal. This indicates that the performance bottleneck is caused by loading and rendering a massive number of requests in a single project.

Cause

Upon investigating the codebase, it appears that the \Sidebar\ collections list renders the tree recursively (\CollectionItem\ renders its children components directly). When a folder containing thousands of requests is expanded, thousands of DOM nodes are mounted simultaneously without any virtualization.

Proposed Solution

Since
eact-virtuoso\ is already a dependency in \�runo-app, we can optimize the \Sidebar\ by flattening the collections tree and using \Virtuoso\ to render only the visible items (Virtual Scrolling).

I have already implemented a proof-of-concept locally that:

1. Flattens the collections tree based on the \collapsed\ state.
2. Replaces the recursive rendering in the Sidebar with <Virtuoso>.

This completely eliminates the UI freeze. I would love to submit a PR for this! Should I go ahead and open the PR for review?

[coderabbitai]

⚠️ Possible Duplicate Issue(s)

• Bruno becomes unresponsive on opening a large collection  #1559

🔗 Related PRs

#6080 - Auto scroll to show this item when its tab becomes active [merged]
#6825 - fix: resolve tab flickering when switching between requests [merged]
#7639 - fix: prevent rerun flicker and fix runner configuration list order [merged]
#7810 - refactor(table): virtualise tables for perf for EditableTable components [merged]
#7861 - fix: collection settings access, UI overflow fixes, and auto-focus URL bar [merged]

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[Rohan-Bruno]

Hi @zhangqxgz, thank you for reporting this issue.

We appreciate you taking the time to bring it to our attention. This is a known issue, and we'd like to gather a few additional details to better understand your setup.

Could you please let us know:

• Which operating system and OS version you're using?
• Which version of Bruno you're using?
• Whether you're using a .bru collection or a YAML-based collection?

This information will help us confirm that you're experiencing the same issue and ensure we're tracking it correctly.

[Rohan-Bruno]

Hi @zhangqxgz, an update on this!

Could you please try our latest nightly build and let us know if you're still experiencing the same issue?

https://github.com/usebruno/bruno-nightly-builds/releases/tag/v3.5.1-2026.07.10

Also, could you enable the File Cache beta feature by going to Preferences → Cache → File Cache and let us know if you notice any improvement in performance?

Your feedback on both the nightly build and the File Cache feature will help us evaluate whether these changes address the issue.

[helloanoop]

@zhangqxgz We are also doing a number of performance optimisations. The caching that Rohan mentioned above should help with subsequent loads.

I have already implemented a proof-of-concept locally that:

Flattens the collections tree based on the \collapsed\ state.
Replaces the recursive rendering in the Sidebar with .
This completely eliminates the UI freeze. I would love to submit a PR for this! Should I go ahead and open the PR for review?

Yes, would love to see the approach you took, could you submit a PR please. Thanks!

[chirag-bruno]

Hello @zhangqxgz, thank you very much for reporting the issue. We are putting some significant efforts into improving the overall performance of the application. This is gonna be an incremental process.

Like @Rohan-Bruno mentioned, we have an implementation in place (beta) in our latest nightly build. We would love to hear your feedback on that.

The virtualisation approach isn't something we have tried and we would love to see an implementation. Please raise a PR and involve me in the conversation. Would be happy to review it and get it to a place that can benefit the product.

Cheers.

[blagasse700]

Hello @Rohan-Bruno ,
I have done a quick test with the build v4.0.0-2026.07.14.

With the "File cache" active, I do not see anymore in the tree collection the symbolic links to folders:

With "File cache" inactive, I could see them:

[chirag-bruno]

Hi @blagasse700, thank you for reporting this! We had completely missed this issue. I've opened a PR that should resolve it.

If you have a chance, could you check out the PR branch, run npm run setup, followed by npm run dev, and let us know if the fix works as expected? We've also added tests to make sure this doesn't happen again in the future.

[blagasse700]

Hi @chirag-bruno ,
I have downloaded your branch, and tried to run the commands that you suggested, but I encountered errors.
I am a newbie for these things.
I will have to discuss with my AI "friends".
=> Sorry, I will have to test this when I will have more time.
But thanks for your quick reaction and feedback.

[helloanoop]

@chirag-bruno Please work with prag and share an experimental build for @blagasse700 to test

[chirag-bruno]

Hey @blagasse700, we have addressed the issue in our latest nightly. You can find this here . Do let us know if this build solves the issue for you.

[blagasse700]

@chirag-bruno
I have done a few tests and it seems to work fine.
Thanks for the quick fix.