Calibre 8.10 Book Viewer not displaying text

institute · 09-21-2025, 09:07 AM

Hi all,

The Calibre 8.10 Book Viewer is not displaying text properly. This is an issue with every book in the Library (all epubs). Instead I just see a wall of question marks each within a square. I have attached a screenshot. These books will display correctly in the Books.app using "Open with." I am on MacOS Sequoia 15.7 using a M2 Mac Mini. The Calibre library is stored on an external hard drive. Other files on that hard drive open properly in their respective applications. I have restarted the computer and reinstalled Calibre to no avail. Any ideas what the issue might be?

Thanks

theducks · 09-21-2025, 10:06 AM

I suspect the viewer has had a Font set to something that does not support your books character set.

With the viewer CLOSED (off)
In the configuration folder:
Rename viewer-webengine.json to viewer-webengine.json.bak

When you next start the viewer, it will be recreated (with default settings).

If this works, make your other setting changes as desired and delete the previous BAK file.

If it does not help and you had customizations you wanted to keep, delete the NEW version, then rename the .BAK (by removing the .BAK part) file to the original

kovidgoyal · 09-21-2025, 10:28 AM

It's likely a bad font in the system, see for example: https://bugs.launchpad.net/bugs/2125179

institute · 09-21-2025, 10:47 AM

Yes. That was it. I had been using Garamond for ages but apparently that font file is suddenly corrupt according to Font Book. I changed the font in the viewer preferences and it works again. Thanks!

KevinH · 09-22-2025, 11:03 AM

BTW, that same bug hit me but the problem was not a bad font, but a duplicate font which seems to confuse Qt. It turns out I had a local Arial font file and a local Times New Roman font file but Sequoia installed a system version of Arial and of Times New Roman with lots of unicode code points added to each of their versions.

With Apple's FontBook I was able to detect the duplicates and remove/disable my own local copies of Arial and Times New Roman and everything Qt started to work again.

So look out for font duplicates as well. If in doubt, disable your local font files.

hlpell · Today, 09:56 AM

I have a macbook air 2022, Tahoe 26.5
Calibre 9.8
Just installed Tahoe and e-book viewer was showing all text as question marks.

Someone suggested I look at the console for error messages. I opened the inspector and selected Console. There were no messages. I selected verbose and went to the Configure Book Reader page -> fonts selection page and randomly selected a ??? font from the dropdown. Hoping that it would trigger an error in the console. No error.
I went back to the book and Hooray! I could read the book.
I restarted Calibre and the reader and then rebooted my Air, and while I can read books again, the Configure book reader is still a bunch of ??????
I'm willing to try other fixes that you might suggest. But at least I can read my books again.
Howard

kovidgoyal · Today, 11:08 AM

Open font book and locate and remove any corrupted font files.

hlpell · Today, 11:24 AM

Thanks for the suggestion but I'm not sure how to do this. I get the fontbook open but then how do I see which font is corrupt?

hlpell · Today, 04:41 PM

Hello Kovid,
It looks like this is a known bug in Tahoe 26.5 and was discovered in beta. Not sure why it shipped with 26.5 but it appears it was. As it is only affecting the fonts in the Ebook reader configuration pages, I can still read books until Apple ships a fix. Here's the link to the bug
https://github.com/soloterm/solo/issues/116
Thanks again for your help.
Howard

09-21-2025, 09:07 AM	#1
institute Enthusiast Posts: 36 Karma: 68 Join Date: Apr 2013 Device: Kobo Libra 2, iPad	Calibre 8.10 Book Viewer not displaying text Hi all, The Calibre 8.10 Book Viewer is not displaying text properly. This is an issue with every book in the Library (all epubs). Instead I just see a wall of question marks each within a square. I have attached a screenshot. These books will display correctly in the Books.app using "Open with." I am on MacOS Sequoia 15.7 using a M2 Mac Mini. The Calibre library is stored on an external hard drive. Other files on that hard drive open properly in their respective applications. I have restarted the computer and reinstalled Calibre to no avail. Any ideas what the issue might be? Thanks Attached Thumbnails Last edited by institute; 09-21-2025 at 09:18 AM.

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09-21-2025, 10:06 AM	#2
theducks Well trained by Cats Posts: 31,778 Karma: 64144480 Join Date: Aug 2009 Location: The Central Coast of California Device: Kobo Libra2,Kobo Aura2v1, K4NT(Fixed: New Bat.), Galaxy Tab A	I suspect the viewer has had a Font set to something that does not support your books character set. With the viewer CLOSED (off) In the configuration folder: Rename viewer-webengine.json to viewer-webengine.json.bak When you next start the viewer, it will be recreated (with default settings). If this works, make your other setting changes as desired and delete the previous BAK file. If it does not help and you had customizations you wanted to keep, delete the NEW version, then rename the .BAK (by removing the .BAK part) file to the original

09-21-2025, 10:28 AM	#3
kovidgoyal creator of calibre Posts: 46,253 Karma: 29630732 Join Date: Oct 2006 Location: Mumbai, India Device: Various	It's likely a bad font in the system, see for example: https://bugs.launchpad.net/bugs/2125179

09-21-2025, 10:47 AM	#4
institute Enthusiast Posts: 36 Karma: 68 Join Date: Apr 2013 Device: Kobo Libra 2, iPad	Yes. That was it. I had been using Garamond for ages but apparently that font file is suddenly corrupt according to Font Book. I changed the font in the viewer preferences and it works again. Thanks!

09-22-2025, 11:03 AM	#5
KevinH Sigil Developer Posts: 9,668 Karma: 6774048 Join Date: Nov 2009 Device: many	BTW, that same bug hit me but the problem was not a bad font, but a duplicate font which seems to confuse Qt. It turns out I had a local Arial font file and a local Times New Roman font file but Sequoia installed a system version of Arial and of Times New Roman with lots of unicode code points added to each of their versions. With Apple's FontBook I was able to detect the duplicates and remove/disable my own local copies of Arial and Times New Roman and everything Qt started to work again. So look out for font duplicates as well. If in doubt, disable your local font files.

Today, 09:56 AM	#6
hlpell Junior Member Posts: 3 Karma: 10 Join Date: May 2026 Device: Calibre V9.8	I have a macbook air 2022, Tahoe 26.5 Calibre 9.8 Just installed Tahoe and e-book viewer was showing all text as question marks. Someone suggested I look at the console for error messages. I opened the inspector and selected Console. There were no messages. I selected verbose and went to the Configure Book Reader page -> fonts selection page and randomly selected a ??? font from the dropdown. Hoping that it would trigger an error in the console. No error. I went back to the book and Hooray! I could read the book. I restarted Calibre and the reader and then rebooted my Air, and while I can read books again, the Configure book reader is still a bunch of ?????? I'm willing to try other fixes that you might suggest. But at least I can read my books again. Howard

Today, 11:08 AM	#7
kovidgoyal creator of calibre Posts: 46,253 Karma: 29630732 Join Date: Oct 2006 Location: Mumbai, India Device: Various	Open font book and locate and remove any corrupted font files.

Today, 11:24 AM	#8
hlpell Junior Member Posts: 3 Karma: 10 Join Date: May 2026 Device: Calibre V9.8	Thanks for the suggestion but I'm not sure how to do this. I get the fontbook open but then how do I see which font is corrupt?

Today, 04:41 PM	#9
hlpell Junior Member Posts: 3 Karma: 10 Join Date: May 2026 Device: Calibre V9.8	Hello Kovid, It looks like this is a known bug in Tahoe 26.5 and was discovered in beta. Not sure why it shipped with 26.5 but it appears it was. As it is only affecting the fonts in the Ebook reader configuration pages, I can still read books until Apple ships a fix. Here's the link to the bug https://github.com/soloterm/solo/issues/116 Thanks again for your help. Howard

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