[Conversion Output] KFX Output

[jhowell]

Originally Posted by tomsem

Kindle Previewer (3.106.0) is giving this error (hence KFX output fails) converting an ePub:

E21018: Enhanced Mobi building failure, while parsing content in the file.

The error message indicates a failure in the kindlegen part of the conversion process. I suspect that it is related to the quote characters contained in the alt text.

I am unable to duplicate the problem. I pasted that code into an EPUB and it converted without error using Kindle Previewer 3.106.

[tomsem]

Originally Posted by jhowell

The error message indicates a failure in the kindlegen part of the conversion process. I suspect that it is related to the quote characters contained in the alt text.

I am unable to duplicate the problem. I pasted that code into an EPUB and it converted without error using Kindle Previewer 3.106.

Visually the exact same alt text is in a nearby <img> tag. But maybe issue presents only with some enclosing block. I’d try sending that but don’t have access to my Mac ATM.

There are 3 of them with this issue in this HumbleBundle offering:

https://www.humblebundle.com/books/t...i-apress-books

Data Engineering With Generative…
From Data to Dollars…
A Guide to Adobe Animate…


The last of these is included in the $5 option.

If you can point me to an obfuscater script/plugin I will try to see if I can supply example directly but not clear obfuscated book would have issue.

Calibre’s editor check finds tons of errors but cannot fix any of them, and the one KP3 complains of is not one of them AFAICT.

Note Send To Kindle complains too as expected (which was source of initial discovery). Never found STK complain if KP3 does not as well.

[jhowell]

Originally Posted by tomsem

If you can point me to an obfuscater script/plugin I will try to see if I can supply example directly but not clear obfuscated book would have issue.

You could try the ScrambleEbook plugin.

I am willing to look at an example that fails if you can provide one, but I am unlikely to be able to do anything about it since it is Amazon’s software that is failing.

[jhowell]

Originally Posted by tomsem

Note Send To Kindle complains too as expected (which was source of initial discovery). Never found STK complain if KP3 does not as well.

You could try conversion of those books to KFX using the kfxgen plugin. That plugin does not rely on the Kindle Previewer. It might also be built-in to calibre in a future release.

You might need to uninstall KFX Output in order to make it work. As far as I can tell calibre does not allow selection between multiple output plugins for the same format and I don't know how it chooses which one to use for conversion.

[tomsem]

Originally Posted by jhowell

You could try conversion of those books to KFX using the kfxgen plugin. That plugin does not rely on the Kindle Previewer. It might also be built-in to calibre in a future release.

You might need to uninstall KFX Output in order to make it work. As far as I can tell calibre does not allow selection between multiple output plugins for the same format and I don't know how it chooses which one to use for conversion.

Thanks, I'll give that a try.

[tomsem]

Originally Posted by jhowell

You could try conversion of those books to KFX using the kfxgen plugin. That plugin does not rely on the Kindle Previewer. It might also be built-in to calibre in a future release.

You might need to uninstall KFX Output in order to make it work. As far as I can tell calibre does not allow selection between multiple output plugins for the same format and I don't know how it chooses which one to use for conversion.

I installed kfxgen, had to uninstall (not just disable) KFX Output. The conversion is very fast, and they seem to open fine on my Kindle.

There are some (I would say numerous) formatting issues that are not present in the original ePub, guessing CSS issues.

(I assume kfxgen is not capable of converting fixed layout ePub, e.g. comics)

However this does not tell me anything about why Send To Kindle and Previewer complain.

If you are curious, I've attached scrambled version of one of the books, which still has the Previewer issue.

[jhowell]

Originally Posted by tomsem

I installed kfxgen, had to uninstall (not just disable) KFX Output.

The next release of the KFX Output plugin will allow switching to kfxgen when it is disabled.

Originally Posted by tomsem

I assume kfxgen is not capable of converting fixed layout ePub, e.g. comics

Yes, as far as I know it only handles reflowable books.

There is however a different project that is supposed to handle comics, kindle-comic-workaround-5.19.x. I haven't tried it.

Originally Posted by tomsem

However this does not tell me anything about why Send To Kindle and Previewer complain.

If you are curious, I've attached scrambled version of one of the books, which still has the Previewer issue.

I took a look at your EPUB and it contains the HTML entities &lt; and &gt; in image alt text which are handled incorrectly by the Kindle Previewer. That is a long-standing bug that is automatically corrected by this plugin before passing an EPUB to the Previewer for conversion.

[tomsem]

Thanks for looking at this, that's easy enough to fix.

I knew about kindle-comic-workaround too but have not tried it, mostly because I prefer to use Kindle Create to be able to tweak things (add ToC and sometimes guided view) and preview result before converting.

I've also seen a project that converts PDF to functional Print Replica KFX but have yet to try that.

[jhowell]

Version 2.20.0 - 22 Aug 2026

Adjust the priority of this plugin depending on whether or not it is disabled in order to allow selection between it and kfxgen for use in conversion if both plugins are installed. calibre must be restarted after enabling or disabling this plugin for the change to take effect.

Detect Kindle Previewer versions up to 3.106.0.

Remove support for calibre versions prior to 6.0. (Older versions of this plugin that work under calibre 2.x through 5.x are available in this post, however the use of those versions is unsupported.)

[Koco]

Originally Posted by jhowell

Version 2.20.0 - 22 Aug 2026

Adjust the priority of this plugin depending on whether or not it is disabled in order to allow selection between it and kfxgen for use in conversion if both plugins are installed. calibre must be restarted after enabling or disabling this plugin for the change to take effect.

Detect Kindle Previewer versions up to 3.106.0.

Remove support for calibre versions prior to 6.0. (Older versions of this plugin that work under calibre 2.x through 5.x are available in this post, however the use of those versions is unsupported.)

Hello, jhowell. I ran into a problem while updating the KFX Output plugin. Calibre reported an error saying:

Traceback (most recent call last):
  File "calibre\customize\ui.py", line 720, in initialize_plugin
  File "calibre_plugins.kfx_output.__init__", line 82, in __init__
  File "calibre\customize\ui.py", line 126, in is_disabled
AttributeError: 'str' object has no attribute 'name'

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "calibre\gui2\dialogs\plugin_updater.py", line 742, in _install_clicked
  File "calibre\customize\ui.py", line 532, in add_plugin
  File "calibre\customize\ui.py", line 727, in initialize_plugin
calibre.customize.InvalidPlugin: 初始化插件 Traceback (most recent call last):
  File "calibre\customize\ui.py", line 720, in initialize_plugin
  File "calibre_plugins.kfx_output.__init__", line 82, in __init__
  File "calibre\customize\ui.py", line 126, in is_disabled
AttributeError: 'str' object has no attribute 'name'
 失败，跟踪：
Traceback (most recent call last):
  File "calibre\customize\ui.py", line 720, in initialize_plugin
  File "calibre_plugins.kfx_output.__init__", line 82, in __init__
  File "calibre\customize\ui.py", line 126, in is_disabled
AttributeError: 'str' object has no attribute 'name'

Could you tell me what's going wrong? I tried manually uninstalling the old version of the Output plugin first, but Calibre said I didn't have it installed. I found the Output folder in the Plugins directory, deleted it, but even after that (and multiple restarts), I still can't install the Output plugin.

*Calibre version: 7.9