The short answer, for the three cases that come up most. Validating one file, right now: run epubcheck — it is free and it is the standard. Need the accessibility verdict the industry recognises: run Ace by DAISY, also free. Answering for a whole catalogue, repeatedly, in language somebody who is not an engineer can act on: that is what a platform is for, and it is what Origami sells.
What follows compares eight tools on the same six criteria, with every fact taken from the maker’s own public pages and dated. Origami is one of the eight, on the same terms as the rest — the section on when not to choose it is not a formality.
How these tools fit together
Two of the eight are not really competitors of the other six: they are the layer the other six run. epubcheck decides whether a file conforms to the EPUB specification, and Ace by DAISY decides whether it meets the accessibility standards. Nearly every commercial tool on this page, Origami included, wraps one or both of them and adds something around the outside.
That is worth saying plainly, because it tells you what you are actually buying. Nobody is selling you a better verdict than epubcheck’s — it is the same verdict. What differs is whether it arrives as a command-line dump or as a prioritised report, whether it covers one file or four hundred, whether anything is repaired afterwards, and whether what comes out is something you can put in front of a retailer.
Where Origami wins, and where it loses
Wins, each one checkable rather than an opinion. It runs three engines and cross-references them into a single verdict, which nothing else on this list does. It works on a catalogue rather than a file. It translates a finding into what it costs a reader instead of quoting the rule that was broken. It has an API, where Sigil, Calibre and PubCoder have none and epubcheck and Ace are command-line tools you would have to wrap yourself. It separates placeholder alt text from missing alt text, which nobody else here distinguishes. And it repairs rather than only reporting, inside a limit it declares.
Loses, and saying so is the point of this page. It does not author or lay out books, where PubCoder and Sigil do. It has no per-retailer rules, where FlightDeck does — a real advantage for anyone distributing to six stores. It does not generate alt text for EPUB, only for PDF. It costs money, where epubcheck, Ace, Sigil and Calibre are free and, for a single file, are the right answer. And it is the newest and least known name here, without the track record of Firebrand or PubCoder.
When not to choose Origami
If you validate a handful of files a month and you are comfortable reading a command-line report, use epubcheck. It is free, it is the same engine we run, and a subscription would buy you nothing you need.
If what you want is the accessibility verdict and nothing else — one file, one report, to send to a partner — run Ace by DAISY. Same reasoning, same answer.
And if your problem is producing the book rather than checking it, with interactive EPUB3, fixed layout or media overlays, you want PubCoder, or Sigil for hand work on a single file. Origami does not lay out books, and a platform that checks files will not help you make one.
The eight tools, side by side
Every entry has the same shape: what it is, the one-line verdict, what it really checks, what it costs and when we checked, who it is for, and where it stops.
Prices and capabilities checked against each maker’s own public pages on August 21, 2026.
How we compared
- What it checks
- Conformance, accessibility, production quality — or nothing at all, because the tool does something else.
- Whether it repairs
- Reporting a problem and fixing it are two different products.
- One file or a catalogue
- The structural difference between a desktop tool and a platform.
- Interface
- Command line, desktop, browser, API — this is what decides who on your team can actually use it.
- Price
- Quoted from the maker’s own page, with the date we read it.
- Who maintains it
- A standards body, a company, or a volunteer project. It is the best available hint at how the tool will age.
| Tool | What it checks | Repairs? | One file or catalogue | Interface | Price | Maintained by |
|---|---|---|---|---|---|---|
| epubcheck | Conformance (EPUB spec) | No | One file | Command line | Free, open source | W3C / DAISY community |
| Ace by DAISY | Accessibility (WCAG 2.1, EPUB A11y 1.1) | No | One file | Command line, desktop app | Free, open source | DAISY Consortium |
| FlightDeck (Firebrand) | Conformance + per-retailer rules | No | File or list | Browser | Not published | Firebrand Technologies |
| Sigil | Conformance while you edit | By hand, by you | One file | Desktop editor | Free, open source | Sigil project |
| Calibre | Nothing — it converts | No | Library | Desktop | Free, open source | Calibre project |
| PubCoder | Conformance + accessibility (epubcheck, Ace) | You author the fix | One file | Desktop + free web checker | From €99/year | PubCoder |
| PaperbackKit | Accessibility, EAA focus | Yes, automated | Catalogue, over an API | Browser + API | Free during beta | PaperbackKit |
| Origami | Conformance + accessibility + 88 production rules | Yes, AI-assisted, within a declared limit | Catalogue, over an API | Browser + API | From $29/month | publica.la |
epubcheck
The canonical EPUB conformance validator, maintained by the W3C and DAISY community. Free, Java, command line.
It is the standard everything else is measured against, Origami included — and it is free. If you can read a command-line report and you validate one file at a time, you need nothing else. It repairs nothing, says nothing about accessibility, and its messages come from the schema validator rather than from a human.
- What it really checks
- Conformance with the EPUB specification, and nothing else. Every finding carries a code, a severity and a file-and-line location.
- What it costs
- Free and open source, BSD-3-Clause.
- Best for
- Anyone validating a file at a time who is comfortable at a command line.
- Where it stops
- No accessibility, no repair, no catalogue — and the messages are the schema validator’s own, so they read like one machine talking to another.
Ace by DAISY
The DAISY Consortium’s reference accessibility checker for EPUB. Open source and free.
It is the accessibility verdict the industry recognises, and no alternative replaces it — they all wrap it. “Ace is currently a command line tool”, in the DAISY Consortium’s own words. It reports; it does not fix; it does not work through a catalogue.
- What it really checks
- Accessibility against WCAG 2.1 and EPUB Accessibility 1.1, with a detailed report per file.
- What it costs
- Free and open source, MIT.
- Best for
- Getting the accessibility verdict retailers, aggregators and libraries recognise.
- Where it stops
- It reports and stops there. No repair, one file at a time, and a command line between you and the answer.
FlightDeck (Firebrand)
A commercial EPUB QA platform that validates against the ingestion requirements of individual retailers.
It has the one thing nobody else here has: per-store rules. It checks against the real requirements of Amazon, Apple, Barnes & Noble, Kobo, Google and NetGalley, not only against the specification. The price is not public, and there is no AI-assisted repair.
- What it really checks
- EPUB conformance plus retailer-specific ingestion rules.
- What it costs
- Not published; quoted on request.
- Best for
- A publisher distributing to several stores who keeps being rejected by one of them.
- Where it stops
- No assisted repair, and no public price to compare against anything on this page.
Sigil
A free, open-source desktop EPUB editor with validation built in.
It is the best tool there is for fixing an EPUB by hand, and it is free. If the problem is one file and you know XHTML, Sigil will save you time. It is not a compliance tool and it does not scale to a catalogue.
- What it really checks
- Structure and conformance as you edit, through an integrated epubcheck.
- What it costs
- Free and open source, GPL-3.0.
- Best for
- Fixing one file properly, by hand, when you know what the markup ought to say.
- Where it stops
- One file and one person at a time. An editor leaves no record you can show anybody.
Calibre
A free, open-source ebook library manager and format converter.
Irreplaceable as a converter and a library; it is not a validator. It earns its place here because half the industry converts with it — and because a Calibre conversion can introduce validation errors you then have to go and find, which is precisely why you validate after converting.
- What it really checks
- Nothing, in the conformance sense. It converts, catalogues and reads.
- What it costs
- Free and open source, GPL-3.0.
- Best for
- Converting between formats and managing a library.
- Where it stops
- A conversion is a new file with new problems. Validate after Calibre, never instead of it.
PubCoder
Desktop software for authoring interactive and fixed-layout EPUB3, with a free online epubcheck and Ace checker beside it.
If your problem is creating accessible interactive books, this is the tool — and its free online checker is the most convenient one on the market. Annual licence from €99. The checker is free for 5 files per session, unlimited with an account, 100 MB per file. It is an authoring tool: it is not a catalogue pipeline.
- What it really checks
- epubcheck and Ace by DAISY, through its free online checker — and the file you are authoring, while you author it.
- What it costs
- Annual licence from €99. The online checker is free: 5 files per session without an account, unlimited with one, 100 MB per file.
- Best for
- Producing interactive and fixed-layout EPUB3 that is accessible from the first page instead of remediated later.
- Where it stops
- A desktop authoring tool. No catalogue pipeline, and no API to drive it from your own systems.
PaperbackKit
A batch EPUB remediation service driven by an API, free while it is in beta.
It is the one tool here competing for the same sentence Origami does — remediating a catalogue over an API — and today it is free. Batch remediation runs over an authenticated endpoint that returns corrected files plus a report per title, and it ships a free EPUB accessibility checker and an EAA guide of its own. It is in beta: free is a stage rather than a price.
- What it really checks
- Accessibility, with an EAA focus, returning corrected files and a report for each title.
- What it costs
- Free during the beta. Two models are announced: pay per book, or API access for a catalogue.
- Best for
- Remediating a backlist over an API while the beta lasts.
- Where it stops
- Beta. The price is a stage, not a commitment, and everything above is read from its public documentation rather than from a run of ours.
Origami
A browser platform that runs epubcheck, Ace by DAISY and the 88-rule Qualebook checklist together, with AI-assisted repair, ONIX export and an API.
It runs the same canonical engines as everything else here, and what it adds is what happens after the report: one verdict, in plain language, for the whole catalogue. From $29/month, measured in publications rather than credits. It is not a layout tool, it has no per-retailer rules, and it does not generate alt text for EPUB.
- What it really checks
- epubcheck for conformance, Ace by DAISY for accessibility and the 88 Qualebook production rules — cross-referenced into a single verdict.
- What it costs
- From $29/month, measured in publications per cycle rather than in per-file or per-image credits.
- Best for
- A team answering for a whole catalogue that needs the answer in language a non-engineer can act on.
- Where it stops
- It does not author or lay out a book, it has no per-retailer rules, and it does not generate alt text for EPUB — it finds the gaps and hands them to a person.