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Detect and repair common EPUB formatting issues
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E-books are more complex than they look. An EPUB is actually a mini-website zipped up — HTML pages, images, stylesheets, and a table of contents, all wired together with a metadata file. When any part of that structure is wrong, readers crash, chapters go missing, or the book looks nothing like the author intended.
The TOC tells your e-reader how to build the chapter list. Without it, readers like Kindle or Apple Books show a blank navigation panel — your readers can't jump between chapters and have to scroll through the whole book.
Causes blank chapter listUnlike a web browser, most e-readers are strict about HTML structure. An unclosed tag, an unescaped & character, or mismatched elements can cause entire chapters to display as a wall of raw code — or not render at all.
Can break entire chaptersThe language tag tells your reader which language the book is written in. Without it, text-to-speech reads aloud with the wrong accent or pronunciation, automatic hyphenation uses the wrong dictionary, and some readers refuse to enable their accessibility features.
Breaks text-to-speechEvery EPUB needs a unique ID — usually a UUID — so stores and reading apps can track it. Without one, your book may sync incorrectly across devices, fail to update after corrections, or be rejected outright by distributors like Smashwords and Draft2Digital.
Causes distribution failuresWhen a stylesheet says color: black or font-size: 14px, that overrides the reader's theme. Night mode stays blinding white. The user's font-size preference is ignored. People with visual impairments lose the accessibility settings they depend on.
Cross-references, footnotes, and "see chapter 4" links all use internal hyperlinks. If a chapter file was renamed, moved, or never included, those links silently lead nowhere — or worse, cause the reader app to freeze on some devices.
Footnotes & cross-refs failThe manifest is a complete list of every file in the book. The spine defines the reading order. If a chapter is in the book's zip file but not listed in the manifest, most readers ignore it entirely. If the spine order is wrong, chapter 6 might appear before chapter 2.
Chapters appear out of orderEach file in an EPUB must be declared with a media-type — basically a label that says "this is an image" or "this is a stylesheet." If the label is wrong (e.g. a JPEG file labelled as plain text), fonts won't load, images won't display, and some validators will reject the book.
Images & fonts fail to loadHTML IDs must be unique — like a person's passport number. When two headings share the same ID, the reader's internal navigation gets confused. Tapping a TOC entry might jump to the wrong chapter, and some devices quietly skip to the first match rather than the intended destination.
TOC jumps to wrong chapterWithout a properly declared cover, your book shows up as a blank grey rectangle in the reader's library. On some storefronts, the cover is pulled directly from this metadata — so a missing declaration means no cover art on the product page, even if the image file is physically present in the EPUB.
Blank cover in libraryConversion tools sometimes generate placeholder chapter files with no content — just an empty HTML shell. These show up as unexpected blank pages mid-book. Readers interpret them as intentional and display them, which can make a book feel unfinished or broken.
Unexpected blank pagesThe first file in every EPUB must be called mimetype and contain exactly the text application/epub+zip — no spaces, no newline at the end, uncompressed. It's how software recognises a file as an EPUB at all. Get it wrong and some readers refuse to open the book entirely.
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