Adobe has always been like this, too. They squandered an enormous marketshare with Flash because the alternative would've been spending a couple million on QA and they managed to unite all of the browser manufacturers in agreement that the web was better off without such an unreliable partner.

I shipped a couple of things on Flash back in the day but it was staggeringly bad software — random crashes, various heisenbugs where changes in one area would affect unrelated functionality in other modules, etc. — and while it cost something like $800, it was completely unsupported: I filed a number of trivially reproducible bugs with reduced test cases but never heard anything back until the next release came out and they sent automated suggestions that the bug might be fixed so I should buy a full-price license and find out.

As someone who has spent a good deal of time trying to build ereader software, eventually I decided to try to deal with the devil and build on top of RMSDK.

There is no way to get access to it. I don't mean the licensing cost is prohibitively expensive for an indie dev although I understand that to be the case as well.

There is no one to talk to. The email listed on their website does not respond to anything. Not even so much as a "Thanks for your interest" or a "We will get back to you".

I messaged a former colleague who worked there to try to see what the process is to get access to rmsdk. He said he tried to find internal docs about it and couldn't find anything.

I tried to find people on linkedin who might be associated with rmsdk and ask them and similarly found nothing.

Meanwhile publishers only distribute most of their titles with one of their known drm vendors ie Apple, Amazon, or Adobe. The other two are entirely closed off.

If this isn't anticompetitive trust behavior, I don't know what is.

Unfortunately, epub and epubcheck isn't the great uncontroversial resource the author makes it out to be. When W3C, Inc. took over maintenance of the EPub spec around when 3.1 was current, they just referenced WHATWG HTML and other ever-expanding browser specs ([1]). Being "living standards", these have no versioning or QA. As a consequence of being based on a version of HTML that redefined headers and sectioning, Epub 3.2 just made existing epubs non-conforming. Which is why Calibre and other tool still recommend 3.1 or better yet 2.

The case mentioned where the CSS min() function is rejected is another place where bulk import of the extremely complex CSS spec is just not helpful. Ebook readers aren't evergreen browsers after all.

[1]: https://news.ycombinator.com/item?id=41326179

AIUI, Kobo devices have a more advanced rendering engine if you name the file with .kepub.epub. (I think it's based on ePub 3?) Not sure if it would fix the problem here. But I personally run ePubs through kepubify (https://pgaskin.net/kepubify/try/) before transferring them to my Kobo.

Sharing my experience as a tinkerer, sideloader, and recent Kobo owner.

I used a Kindle for ages, always in airplane mode and only sideloading content. Honestly, it was a pretty good setup.[1] But it seemed like it would be harder to setup this way on newer devices, so when mine finally failed, I got a Kobo Clara BW. I was thrilled I could boot it up in "sideloader mode" and not even register it or enable wifi.

I noticed poor typography on my epubs, learned about converting to kepub so I did that (which helped). It was a familiar flow to what I was used to converting to azw3 for the Kindle. My remaining typography gripe with kepubs is that it treats a word+em-dash as a word for inserting space in full justification. Em-dashes generally don't have spaces on either side, this often looks like a space has been inserted only to the right of the em-dash.

I went down the rabbit hole of NickelMenu and other readers including KOReader and Plato, and even tried (and mostly failed) to vibecode my own opds client app. (because KOReader which has one built-in felt overwhelming)

My current sense is the device feels so much more like it is mine. I have much more flexibility to tinker with it. It is not as polished as the Kindle and the Adobe rendering feels stupid, but that's also a sharp edge that only the side-loading community will hit, most of whom use Calibre which can auto convert to kepub for them. Everyone else is buying books from the Kobo store and getting them delivered as kepubs.

So in the end, I'm a big fan of the Kobo devices.

[1]: Except you cannot remove a wifi password if you aren't in range of that wifi signal. I had a rude experience when my two-year-old was fiddling with my Kindle at my in-laws' house and turned on the wifi where there was still a saved credential. An update triggered immediately and I was frustrated for days that everything in the UI changed.

BTW for those who are looking for a device, the PineNote exists:

https://pine64.org/devices/pinenote/

More expensive and less out-of-the-box software, but straight to the point on device ownership/what kind of software you can run, fewer strings attached.

[EDIT]

Great experience blogs on the PineNote

https://shom.dev/posts/20250308_pinenote-day-one/

https://shom.dev/posts/20250406_a-pinenote-only-5-day-weeken...

Kobo is actually in the process of completely rewriting their e-reader software (you can download the beta in the EU), and I’m pretty sure it’s no longer based on RMSDK. Adobe basically handed the EPUB DRM market to LCP on a silver platter by being a poor maintainer and then selling off to a third party that had botched the migration and further angered end users and platforms, that are switching off Adobe faster than ever

Adobe Digital Editions and RMSDK were recently sold to Wipro Engineering: https://helpx.adobe.com/enterprise/kb/eol-faq-adobe-digital-...

Be happy your readers use an ePub reader that supports (or at least, ignores) something like `max-width` in the first place :-P.

TBH i've being using an ePub reader that i occasionally had to edit ePub files so i get rid of the superfluous styling that made it either not work or show things weirdly/wrong and i've heard comments from others that a bunch of files i had no issues with personally were unreadable for them, which makes me think that unless you really and absolutely need any fancy formatting (i.e. math stuff that can't just be made images - and you really tried to!) then you should stick with the most basic HTML imaginable - things that not even IE4 would render (too) wrong.

And in turn, since i doubt this will ever happen, i sometimes ponder making an "epub reconstruct" tool that attempts to reconstruct epubs so that they use the simplest HTML/CSS :-P (ideally configurable for maximum compatibility).

> When I started out, I dreaded the moment when I hit the validate button on my finished book after months of work, because it would always find something to cry about.

I remembered one particular master student on the verge of tears trying to compile his LaTeX thesis draft, he took the “write and think about formatting later” too literally and was trying to compile it for the first time very close to the deadline.

I understand the frustration of the author but how many readers do have an old, unupgraded, maybe unupgradable epub reader? If authors want to make their work available to all readers they have to build for the least common denominator. If it happens to be something from 2013, sorry but that's the reality of the market.

When building EPublish ( https://frequal.com/epublish/ ), an HTML-to-epub converter, I faced similar hurdles. Trying to keep compatibility with numerous e-readers built with different stacks and varying degrees of EPUB versions is frustrating.

I used EPublish for my first novel, Means and Motive, just published here, DRM-free: https://www.amazon.com/dp/B0GYCZJVGX

So far I haven't heard of compatibility issues, so I think EPublish has hit the sweet spot of EPUB targeting. I agree, however, that it feels like the old days of targeting IE6 on the web. Old readers still exist out there, so we have to aim for the lowest common denominator.

Mentioned at the end, but Kobo's gel better with the KEPUB format. Calibre has a nice converter for this (I think it may be built-in now or still a plugin), but works great. Got a Kobo Clara Colour about ~2 years ago now and I couldn't highlight across pages until I bulk converted my library to KEPUBs. After that, you'd never know there was an issue. This post makes the whole mess make a lot more sense now.

When using Kobo readers, using Calibre and Kobo utilities, which transparently "upgrades" your ePUBs to KePUBs without altering the copy on your disk is a must, and a huge win.

Kobo's added features on top of ePUBs are nice, and their renderer is much better than Adobe's standard pipeline.

So, it's a free upgrade with a terrific local library added on top.

I recently was in the market for a new e-reader and steered away from Kobo and Kindle because of their non-free ecosystem. I don’t know how exactly it would negatively impact me but I didn’t want to find out.

Got a refurbished pocketbook in the end and very happy with it, it reads all imaginable file formats and I can just send books to it via email or cable.

> that bloated pinnacle of software that is 80% about DRM, 20% about the reading experience

I have never seen someone explain the adobe software so perfectly. Using any adobe software is exactly this.

I use KOreader on my Kobo, which is an alternative open-source ebook renderer. It installs pretty easily without rooting the device. In addition to better standards compliance it also is a lot more performant and has niceties like auto cropping of PDFs.

This was originally posted with the full title, which made sense. Why was it truncated?

If you use a kobo you have to give koreader a whirl! The only thing missing for me is the unified view of the library: koreader requires you to navigate to the subdirectory to open your ebook whereas nickel (kobo’s UI) will list them all in one library regardless of how deeply nested they are.

Everything else is better with koreader and it’s super easy to install alongside nickel. And it works very well with calibre + the kobo plugin.

"Epubcheck does basic CSS checking of course, but it can’t validate CSS against a renderer which is fundamentally broken!"

According to the author, Kobo uses CSS from 2013. A quick check with an AI says RMSDK supports CSS 2.1 and parts of 3.

So it's not that the renderer is broken, it's that he believed that epubcheck actually checks against devices and the versions of CSS that those devices support.

This is exactly the issue with test tools: the test tool tests to a spec, but the platform is the gold standard. If you don't like it tough shit.

epubcheck doing its job perfectly while Adobe's ancient RMSDK (frozen somewhere around 2013) silently chokes on valid CSS4 like min() is peak digital publishing pain. The fact that Kobo routes normal .epub to the Adobe engine and only .kepub.epub gets the modern WebKit one feels almost malicious.

If nobody is able to implement the standard it is probably not amazing.

I once read an ebook that was formatted by a guy who had only ever done magazines and it was a huge mess. 2 columns of text per page. No auto scaling.

The best ebook format I have ever experienced is .txt and just let the software figure out where the text needs to go.

> Epubcheck does basic CSS checking of course, but it can’t validate CSS against a renderer which is fundamentally broken!

But isn't that kind of the point of epubcheck? It's surely not intended to validate all of CSS, it's intended to validate that an epub will work... and not working on Kobo devices (probably #2 manufacturer of ebook readers?) is a major issue.

EPUB: the open standard where "valid" and "will render correctly" are two separate hobbies.

I wonder what this writer's ePub are like.

I can't tell what the writing or design are like, because the article renders as a blank page on my old iPad.

Also on my 2026 Kindle Paperwhite.

It's futile to be old man yelling at cloud on HN, but I'm still irritated by web pages that are essentially text, yet can't be bothered to actually display anything. A blank page.

Presumably ePub publications are easier to QA than web pages. They must conform to a subset of web standards.

For my free novels which I deliberately keep the styles to header2 and body text, it is surprising the amount of crud that all the ePub conversion softwares generate, especially since they are just zipped web-pages.

These days I usually get 90% of the way on google docs, then do the final editing on LibreOffice which can add things like tables of contents and cover image, if it opens on Kindle, Kobo and Calibre I consider it job done.

I’m supposed to be able to lend ebooks from my local library. Adobe makes it impossible as their software doesn’t run on my macbook…

Is there a way to root the kobo and put a modern renderer in place?

It's always CSS.

Every Kobo reader is capable of running KoReader ( http://koreader.rocks/ ). That's the first, and probably last, step I'd take to render a book that the default reader takes issue with.

BOOX works fine. One solution is to ask Codex to reformat your epub file before importing it to your ereader.

"EPUB is an amazing open standard for ebooks, and yet so many implementations of it are just fundamentally flawed, all in the name of keeping IP lawyers happy."

Easy to be dismissive, but IP violations can cost a large company hundreds of millions.

IP lawyers are more important to many companies than their software developers.

If you doubt that, check to see who gets paid more...

The author says that "In a perfect world, RMSDK would just stop living in the CSS stone-ages or at least provide some kind of error handling instead of dropping the whole book, but I’m not holding my breath."

This is blatantly wrong.

In a perfect world, RMSDK wouldn't exist in the first place and Adobe would have gone bankrupt and become history at least 10 years ago.

imho for a standard epub there should be as little CSS as possible

Death to Adobe. For this reason and 10,000 others.

ePub compatibility issues are one of the worst parts of having a Kobo reader. I genuinely miss my Kindle and its simple but reliable MOBI format. At least there everything worked

I’m curious if simply running the original EPUB through Kepubify fixes the problem.

https://pgaskin.net/kepubify/

Hot take: you don't need CSS in your book, a few of <style:'width: 100%;'> is enough.

The TLDR version is Abode supports backward compatibility ... and epub - * International Digital Publishing Forum* - is playing with a sprawling mess opting for the race to the top newest standards ... that always works so well and ensures the user base is always upgrading.

I'm very grateful for this information and it explains why I've avoided epub opting for pdf over epub as my reader software is old.

I'm am very much on the side of supporting backwards compatibility. It reminds me of the times the M$ used to upgrade their doc standards ... where if one hadn't upgraded, well bad luck.

>but it can’t validate CSS against a renderer which is fundamentally broken!

The epub standard doesn't say what version of CSS must be supported. There were no guarantees modern CSS would work so I wouldn't call the renderer broken.

I don't like .epub. I understand the reasons why this format exists, and I am 100% behind those reasons. But it's because I don't find any EPUB readers appealing to me. Just give me a FoxIt Reader clone for .epub, that's all. But naaaah!!, every single fucking e-pub reader that I tried must be a fucking library collector instead, like it's 2000's Windows Media Player style. I hate that.

As such, whenever I get my hands on an .epub file, I go to an online converter, convert it to a .pdf file and nuke it from my system. Then the .pdf gets opened in my FoxIt.

Is it just more or hn has become a place to come and complain and consume tech drama disguised as a tech forum? It's all "I hate dario ", "I hate altman", "corporations are evil".

It's getting very tiresome.

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Wow. This brings up some (bad) memories of working with an .epub export about 10 years ago. We had some embedded fonts to work around some poor rendering in some of the readers we tested, but some of the readers ignored the fonts altogether, causing the content to render boxes (bangs head on table)

It looks like not a whole lot has changed in that space -- the readers are still the gate for what you can do with the format. Who's available to make a CanIUse for epub readers, to shame them into compliance? (only partly /s)

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bro, what an anchor to the past that framework is