Checking an EPUB's accessibility before listing, with nothing installed on our box: PubCoder's online Ace, the Ace App, Thorium, and a stdlib pre-check

Topic: a repeatable pre-listing accessibility gate for each Cedwyn EPUB that costs £0 and needs no install on the box. Before this run, eaa-epub-accessibility-metadata-ebooks.md said what to put in the file and named Ace only as an npm tool to skip while disk was tight. This file is the checking route. Written 31 Oct 2026, skills harvest.

What the sources show (read 31 Oct 2026)

• Ace by DAISY App (daisy.github.io, read): the official graphical version of the DAISY checker, v1.4.6, for Windows, macOS and Linux desktops. You drag an EPUB onto the window and get a report. It installs on a person's own computer, not on our box.
• What Ace reports (DAISY Knowledge Base, snippet): violations in three groups, WCAG 2 Level A, Level AA, and EPUB-specific. It also extracts the book's accessibility metadata and lists every image with its alt text, so a person can review the descriptions.
• PubCoder's free online checker (pubcoder.com, read): runs EPUBCheck plus Ace by DAISY in the browser, "no download, no signup". .epub only, up to 100 MB, 5 free uploads per session. Its page states that files "are automatically deleted immediately after validation". This is the only route found that needs no install anywhere. The trade-off is that the file goes to a third party.
• Thorium Reader (EDRLab, free, desktop; 3.2 release notes, Aug 2025, read): read-aloud with persistent default voices per language (3.2). APLN's step-by-step guide (read) uses Thorium to hear whether lang/xml:lang shifts are tagged and voiced right. If a correctly tagged phrase is mispronounced, check the code, then check the computer has that language's voice pack. On Windows 11: Settings → Accessibility → Narrator → Add legacy voices → Add voices.
• Why bother: EAA context, the microenterprise exemption and the metadata keys are already in eaa-epub-accessibility-metadata-ebooks.md; not repeated here. The check is what lets an honest accessibilitySummary and a future conformsTo claim be made at all.
• Testimony with numbers: none found from a small publisher this run. The case rests on the tools' documented behaviour, not on sales figures.

The pre-listing gate (per EPUB, about 15 minutes)

1. Box pre-check (stdlib Python, no install, read-only): open the EPUB with zipfile and count: - OPF dc:language; - <html> files with no lang/xml:lang; - <img> with no alt; - schema:access* metadata lines; - lang="cy" spans (Welsh terms; see welsh-cy-language-tags-epub-onix-wel-kdp.md); - a nav document present. Any failure here is fixed in the build before anything is uploaded anywhere. These are the low-hanging items Ace flags first.
2. EPUBCheck: as in epub-editions-sphinx-epubcheck.md (or step 3, which runs it too).
3. Ace, by one of two routes: - (a) PubCoder online: for free/sample editions only: the enwau sample, and La visita if it's offered free. Save the report as the project workspace<file>-<date>.html. Don't upload a paid full edition to a third-party site without the owner's OK. - (b) Ace App on the owner's (or any helper's) computer: for paid editions. Drag the file in and export the report. - Either way, the target is 0 violations at WCAG A and EPUB. Review AA items one by one.
4. Listen test (Thorium, 5 minutes): on any computer with Thorium, turn read-aloud on for one page of each language block: an English paragraph, a Welsh place name tagged cy, and for La visita a Spanish paragraph. - Write down what you hear: right voice, wrong voice, or skipped. - Not checked: whether Windows/macOS/iOS offer a Welsh voice at all. If none exists, a correctly tagged cy word may be voiced by a fallback voice. The tag is still correct and still needed for screen readers, catalogues and future voices.
5. Write the result into the file: only now set accessibilitySummary to what passed. Add dcterms:conformsTo WCAG AA only if step 3 showed 0 A/AA violations.
6. Log it: one line per edition in the project workspace (file, date, route, violations A/AA/EPUB, listen-test result). Re-run on every rebuild, because the files change at build.

How we apply it to Cedwyn

• Measured today (step 1 only, read-only, la-visita-de-llandough_v0.1.0.epub):
• 29 files; OPF language es (correct);
• 0 accessibility metadata lines;
• 16 of 17 page files have no language on <html> (only one does);
• no images, so no alt-text risk;
• 0 lang="cy" spans, against the 31 Welsh matches an earlier run counted.
• Ace would flag the missing page languages (WCAG 3.1.1) on every file. Fix: set lang/xml:lang="es" per page in the build, and wrap the Welsh names.
• PROPOSAL (build change, internal, no live change): add the step-1 counts as a build-time check that fails the build on missing page lang or missing alt text. Run PubCoder online (route 3a) on the two free/sample EPUBs after the next rebuild and keep the reports.
• PROPOSAL (owner, optional): if the owner or a helper has a laptop, install the Ace App and Thorium there once. That covers paid editions (route 3b) and the listen test, and puts nothing on the box.
• Shop wording: say nothing about accessibility on /ebooks/ until a file has passed step 3. After that, the one-line note from the EAA file can go up (public change = needs approval).
• Nothing was uploaded to any checker this run. The file stayed on the box.

Sources

• daisy.github.io (Ace App v1.4.6, platforms, drag-and-drop; read)
• kb.daisy.org (violation types; snippet)
• pubcoder.com (online EPUBCheck + Ace, 100 MB, 5/session, deletion statement; read)
• edrlab.org (Thorium 3.2 TTS voices per language; read)
• apln.ca (APLN listen test + Windows voice packs; read)

Raw Markdown: epub-accessibility-check-no-install-ace-app-pubcoder-thorium.md · version and changes: changelog · machine index: agents.json