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Kindle compatibilty #8
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Hi,
I have no Kindle so I cannot check it out myself, but I know it works on Kobo-KoReader.
Still I looked it up on the internet.
As far as I understood the Kindle needs 4 font-variants of the same font, be placed in the folder.The official info is:
Note: In order for the Kindle to recognize which style the font has, the fonts must comply with these conventions: Fontname-Regular.ttf (normal) Fontname-Italic.ttf (italic) Fontname-Bold.ttf (bold) Fontname-BoldItalic.ttf (bold and italic) If the font is copied to the device and does not correspond to this naming scheme, the Kindle will not recognize it.This means you first of all have to name the font like "Fastfont-Regular.ttf".
I also read somewhere that the kindle (dependend on the firmware version) needs exactly this 4 names.
Since we have Regular and Bold combined in the FastFont you have to copy the Font four times and name it differently - Regular, -Italic, -Bold and -BoldItalic like mentioned above.Afterwards the Kindle should at least show you the font in the selection menu.
You have to try out if the speed-reading functionality works. That is dependend on, if the kindle supports the opentype features of the font, that are the intelligence to print certain letters bold for speed-reading.It would be great if you could post a short comment, if it worked or not.
That could help other users trying the same ;-)Thanks for your response!
I'll definitely try adding the 4 variants.
Some interesting findings I made last week:
- The two regular files work out of the box on Kindle but only with DRM books, in this case, those purchased directly on the Amazon store.
- Local books pushed to the Kindle via Calibre doesn't allow the font change
- Removing the DRM or converting them to AZW3/Mobi unlock the font change feature
- "Baking" the font in Calibre editor doesn't work too, Kindle overrides it
Hopefully I can find a solution and open up a PR with the fix
Thanks for the amazing work, I've been reading waaay faster and I can understand a lot more than before
I can verify that the font worked straight out of the box with Kindle Paperwhite (5th gen) by copying
Fast-sans.ttfandFast-serif.ttfas they are.I can verify that the font worked straight out of the box with Kindle Paperwhite (5th gen) by copying
Fast-sans.ttfandFast-serif.ttfas they are.Hi, I am using Paperwhite 7th generation, but I cannot find the font after transferring to the font folder.
Update: I finally successfully transferred the font files to the Kindle, however, when I apply the font, it is just plain Sans and Serif
Same @GoSuToSaKuRa
It works great with books purchased directly from Amazon.
For books sent via Calibre:
- MOBI files doesn't show the fonts
- AZW3 files, show the fonts, but it doesn't have the effect, looks like a regular font
I've been trying a lot of things, from "burning" the font directly into the AZW3, custom CSS and nothing works.
Only PDF files with the incrusted font works, but they look horrible on KindleI just created a Python script that applies this effect directly to the files:
https://github.com/arcanite24/libre-bioreadReacted by Sergey ChernyaevCan confirm this works out the box for me too, copying the two files (
Fast-sans.ttfandFast-serif.ttf) over to my Kindle Paperwhite 6" 👌 Thanks!I made a python script that reads the books in your Calibre, let's you choose which ones to convert, and runs @arcanite24 script automatically: https://github.com/giutala/calibre_bionic_converter
Reacted by Born2Root and Sergey ChernyaevJust uploaded the for files with the names you posted and it worked with Calibre loaded epubs without any issue!
Hi, am I right to understand that it is impossible to use this font without converting books with a script?
Amazon Kindle Paperwhite 7th Gen
With books downloaded from the store everything works. Books downloaded through Calibre do not display the font. Is there no solution to this problem?Will this font be supported on the BOOK Go 6 e-reader? I tried adding this font, the system recognizes it, and I can even change the interface font, but when opening a book, it does not display correctly and looks like a regular font. Thank you for your response! P.S. The language I read in is Ukrainian.
- added a commit that references this issue
on Oct 6, 2025 I created my only family of fonts in the PR above but was only able to make them work correctly on older kindles by converting my files first to KFX format using the KFX input and KFX output plugins.
You cannot send these to kindle via calibre, it won't pick up the KFX format, but you can save to disk from the right-click menu and from there select the kindle as the disk location.
For anyone struggling with bionic reading on Kindle (especially Calibre-converted books):
Font-based solutions don't work because Kindle strips OpenType features. The fix is to modify the HTML directly.
I made a browser-based tool that:
- Takes an EPUB, extracts HTML files
- Wraps word beginnings in
<b>tags - Repacks as EPUB
- Works 100% offline, no server needed
https://gist.github.com/ArseneVrnd/0419ae671ff309b90be86d7d930b157f
Just open the HTML file in any browser, drop your EPUB, and download the converted version. Then convert to AZW3 via Calibre for Kindle.
Settings: adjustable bold ratio (20-70%) and minimum word length.
- Kindle paperwhite
- Kindle 5.12.5
- Calibre 5.38
I had same issue where
.azw3did display bionic font options to apply on kindle, however, didn't apply boldness for letters once selected.
Converting files to.kfxresolved it.
Though, this required installing:- KFX Output plugin for calibre
- Kindle Previewer 3.102.0
Reacted by Ceyhan Bekiroglu and MSPaintRoseI got it to work by doing following:
- follow all steps on how to put the fonts on your kindle
- download the KFX output plugin from the calibre plugin store.
- download the kindle previewer 3 from amazon or else the conversion will fail.
- convert your book to KFX
- sideload it via calibre
- select the font you previously put into the font folder
Hi!
Is this compatible with Kindle?
I'm putting the .ttf files into the /fonts directory and they're not showing up