debugManifest stopped working today

[lhdeveloper]

Target SharePoint environment

SharePoint Online

What SharePoint development model, framework, SDK or API is this about?

💥 SharePoint Framework

Developer environment

macOS

What browser(s) / client(s) have you tested

• 💥 Internet Explorer
• 💥 Microsoft Edge
• 💥 Google Chrome
• 💥 FireFox
• 💥 Safari
• mobile (iOS/iPadOS)
• mobile (Android)
• not applicable
• other (enter in the "Additional environment details" area below)

Additional environment details

• browser version - 148*
• SPFx version - 1.21.1
• Node.js version - 22

Describe the bug / error

I was developing locally today, as I do every day, using the parameter in the URL "?debug=true&noredir=true&debugManifestsFile=https://localhost:4321/temp/build/manifests.js"

and suddenly it stopped working.

The authorization message for loading scripts doesn't appear,

there are no calls to localhost being made.

I tested it on different tenants, on different computers, it simply seems that the feature stopped working.

I read that a debug toolbar was implemented at the end of January, and I don't know if there have been any changes today regarding the parameters we use in the URL, but it definitely stopped working.

My manifest is loading correctly on localhost, my certificate is also okay, it simply stopped working starting at 6 PM today (Brazil time).

Does anyone have any information about this?

Steps to reproduce

1. start application
2. apply params on sharepoint url site
3. nothing happens

Expected behavior

so that it would start working again as it always had, recognizing the application running locally.

[Ashlesha-MSFT]

Hello @lhdeveloper,
Thank you for bringing this issue to our attention. We will look into it and get back to you shortly.
If you don’t receive a reply within two working days, please use this escalation form to escalate.

[HarminderSethi]

For me the issue is happening with fast-serve only and local host is not running. But with gulp serve, things are working fine.

[Ashlesha-MSFT]

@lhdeveloper,
Thank you for reporting this issue. We were able to reproduce the problem on our end.
Findings:

Local dev server and manifest serve correctly; workbench loads debug components as expected
On modern pages, the debugManifestsFile parameter is not triggering the authorization dialog or loading debug components
CSP header includes localhost:4321 but no actual requests to localhost are made
We have raised an internal bug with the engineering team for further investigation. We will update this thread once we have more information from them.

[lhdeveloper]

For me the issue is happening with fast-serve only and local host is not running. But with gulp serve, things are working fine.

Yes, I was running Fast-Serve too, but I updated to version 1.22.1 and ran it with the new structure in Heft, and the same thing happened.

Let's wait for a response. Apparently something did happen.
I also opened a ticket with MS for analysis.

[juliemturner]

I'm seeing this too, same configuration as the original poster.

Not running fast serve or any other add-on that isn't standard.

[salleslucas]

SPFx version: 1.21
spfx-fast-serve: 4.0.2
spfx-fast-serve-helpers: 1.21.1
Node: 18.20.8
Browser: Chrome (corporate environment)
Tenant: SharePoint Online (Microsoft 365)
Confirmed behavior: Same issue here. The webpack dev server (fast-serve) compiles successfully on every save (~1s rebuild, no errors), https://localhost:4321/temp/manifests.js is accessible and returns valid content, but SharePoint Online modern pages completely ignore the debugManifestsFile parameter — no requests to localhost are made at all, even with &bypassSW=true appended to the URL.

Tried:

Unregistering the odspserviceworkerproxy.aspx service worker
Enabling "Bypass for network" in DevTools
Using 127.0.0.1 instead of localhost
Running gulp trust-dev-cert
Disabling SWC compiler in fast-serve config
None of the above resolved the issue. The workbench (/_layouts/workbench.aspx) still works as expected.

This started happening around early March 2026. Would appreciate any update on the fix timeline.

[murchelon]

Hi guys, we are also experiencing this issue. It happens with both GULP and HEFT. I've tried running projects ranging from Node 10 to Node 22 with the latest SPFx framework, and the result is the same: we don't get the warning to load the manifest file, and the web part doesn't appear in the list.

I've noticed that the manifest file moved from /temp to /temp/build.

[lhdeveloper]

Currently, only the workbench is functioning.

[lhdeveloper]

Apparently the problem has been solved, everyone.