How do I edit an EPUB file?

Open the EPUB in Sigil (free, Windows/Mac/Linux) — it shows the HTML chapters in a tree view; double-click any chapter to edit HTML directly. Or use Calibre's built-in EPUB editor (right-click the book → Edit book). Both tools let you edit content, fix headings, correct metadata, and update CSS. For quick metadata edits only, Calibre's metadata editor is faster.

Can I edit an EPUB in Sigil for free?

Yes. Sigil is free and open-source. Download from sigil-ebook.com. Open your .epub, then use Book View for WYSIWYG editing or Code View to edit raw HTML. The Table of Contents editor lets you rebuild the NCX/Nav. Sigil is the most capable free EPUB editor for content changes, structural fixes, and CSS cleanup.

How do I change EPUB metadata (author, title, ISBN)?

In Calibre: right-click the book → Edit metadata (shortcut: E). Change title, author, series, ISBN, publisher, language, and cover image. Click OK and then save — Calibre writes the new metadata into the OPF file. In Sigil: go to Tools → Metadata Editor. For command-line, use ebooklib in Python to read and write the OPF metadata directly.

How do I fix heading structure in an EPUB?

Open the EPUB in Sigil or Calibre's book editor. In Code View, find the chapter HTML files and change tags to – where headings should be. Then rebuild the Table of Contents (Sigil: Tools → Generate Table of Contents). Proper heading structure (H1→H2→H3 hierarchy) is required for screen reader accessibility and EAA/WCAG compliance.

How to Edit an EPUB File — Sigil, Calibre, and VS Code

An EPUB is a ZIP archive containing HTML, CSS, and image files. You can open and edit one in several ways depending on what you need to fix — from a simple heading tweak to a full layout overhaul.

What's actually inside an EPUB?

An EPUB file renamed to .zip can be extracted with any archive tool. Inside you'll find:

OEBPS/ or similar — folder containing HTML content files, CSS stylesheets, and images
content.opf — the package manifest (metadata, spine order)
toc.ncx or nav.xhtml — the table of contents
META-INF/container.xml — the entry point that points to content.opf

Option 1: Sigil (best dedicated EPUB editor — free)

Sigil is purpose-built for editing EPUB files. It is free, open source, and available for Windows, Mac, and Linux.

Download from sigil-ebook.com
Open an EPUB directly — Sigil shows the book tree, HTML editor, CSS editor, and live preview side by side
Edit HTML content with syntax highlighting
Fix metadata (title, author, language, publisher) from the Metadata editor
Search and replace across the entire book
Run EPUBCheck validation to catch errors before publishing
Supports EPUB 2 and EPUB 3

Best for: fixing heading structure, editing body text, correcting chapter titles, updating metadata, cleaning up CSS styling.

Option 2: Calibre's built-in editor

If you already have Calibre installed, it includes an EPUB editor.

Right-click any book in your Calibre library
Choose Edit book
The editor opens with a file tree, HTML/CSS editor, and preview panel
Similar to Sigil but with tighter Calibre integration (metadata syncs to your library)

Calibre's editor is less polished than Sigil for heavy editing but convenient if you're already in Calibre managing your library.

Option 3: VS Code or any text editor (manual)

For quick edits, you can work directly with the unzipped files:

Rename book.epub to book.zip
Extract the ZIP
Edit the HTML/CSS files in VS Code (install the EPUB Viewer extension for preview)
Re-ZIP the folder — but be careful: the mimetype file must be the first file in the archive and must not be compressed

The re-zipping step is fiddly. On macOS/Linux:

cd extracted_epub_folder
zip -X0 ../fixed.epub mimetype
zip -rX9 ../fixed.epub * --exclude mimetype

On Windows, use 7-Zip: add mimetype first with no compression, then add the rest.

Common things people edit in EPUBs

Heading hierarchy — change <h2> to <h1>, fix chapter titles
Metadata — correct author name, title, language code
Styles — remove hard-coded font sizes, fix margins, remove page breaks
Table of contents — add missing entries, fix broken links
Alt text — add accessibility alt attributes to images
Footnotes — convert plain text footnotes to proper EPUB aside elements

When manual editing is not the right tool

Manual editing in Sigil works well when you know exactly what to fix. It becomes impractical when:

The source EPUB has hundreds of structural issues from a poor PDF conversion
The document needs to pass a specific compliance standard (Section 508, EPUB Accessibility 1.1)
You need a second pair of eyes to read the whole book and catch all problems

In those cases, consider Premium Verification — a human reviewer reads the full EPUB, applies fixes, and returns a publication-ready file within 24–48 hours.

Need an EPUB from a PDF first? Start with a free conversion.

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