Safari: 'Bad Request - Request Too Long' HTTP 400 error

Question

hmsmoliar Author

Level 1

12 points

Safari: 'Bad Request - Request Too Long' HTTP 400 error

Yesterday, Safari rejected a site that I use daily with the following message:

Bad Request - Request Too Long

HTTP Error 400. The size of the request headers is too long.

I tried this:

1. In Safari, choose Safari → Settings from the menu bar.

2. Open Privacy.

3. Click Manage Website Data…

4. In the search field, enter the site’s domain—for example, example.com .

5. Select every matching entry for that site, including related sign-in domains if they clearly belong to the same service.

6. Click Remove, then Done.

7. Quit Safari completely with Safari → Quit Safari (or Command-Q), reopen it, and visit the site again.

8. Sign in again if needed.

No luck.

The site opens on my other computer with Safari. The site opens with Firefox on my main computer. The site opens with Private Window on my main computer Safari.

Any thoughts?

Thanks

H

Mac Studio, macOS 26.6

Posted on Sep 10, 2026 7:34 AM

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Answer 1

VikingOSX

Level 10

129,722 points

Sep 10, 2026 8:51 AM in response to hmsmoliar

Quit Safari. Press and hold the shift-key when relaunching it. I would clear the browser cache and all history.

If you have enabled the Safari Developer menu item from its Settings > Advanced : Show features for web developers, then you can press option+cmd+E to clear the Safari cache. Combined with the history removal, all cookies will be gone.

If you are using a old http bookmark to that website, something may have changed on that server side that is now rejecting that old client-side bookmark syntax. If this is the case, I would avoid the bookmark and manually visit that basic web server address and build up a new https URL based on that sites current content structure. If that new URL works in a new browser tab, then replace the old bookmark with the new URL construct.

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Answer 2

hmsmoliar Author

Level 1

12 points

Sep 12, 2026 7:02 AM in response to hmsmoliar

So, in the above steps that I tried, I went back and tried

3. Click Manage Website Data…

4. In the search field, enter the site’s domain—for example, example.com .

5. Select every matching entry for that site, including related sign-in domains if they clearly belong to the same service.

6. Click Remove, then Done.

It turns out that I hadn't found the right thing to remove.

Now it's all working again.

Thanks for your thoughts and help.

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Answer 3

VikingOSX

Level 10

129,722 points

Sep 11, 2026 6:01 AM in response to hmsmoliar

What is different in the Safari settings between this Mac's Safari and the Safari on your other Mac where this site URL works as expected. The devil is in the details… Are you using a VPN on one Mac and not on the other… etc?

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Answer 4

hmsmoliar Author

Level 1

12 points

Sep 10, 2026 10:20 AM in response to VikingOSX

Tried all of that and threw in a restart as well. No luck.

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