What is Sigil and what can it do?

Sigil (sigil-ebook.com) is a free, open-source EPUB editor for Windows, macOS, and Linux. It lets you edit chapter HTML files in WYSIWYG or code view, run find-and-replace across all files using regex, generate and edit the table of contents, edit OPF metadata, add/remove images and fonts, split chapters, and apply font obfuscation. It's the standard tool for professional EPUB editing and publishing.

Is Sigil better than Calibre for editing EPUBs?

For editing, yes — Sigil is purpose-built for EPUB editing and has better code view, regex search across all files, and TOC management. Calibre's Edit Book is adequate for quick fixes but Sigil is faster for extensive text work. For conversion (MOBI to EPUB, PDF to EPUB), Calibre is better. Many publishers use Calibre for conversion and Sigil for editing.

How do I generate a table of contents in Sigil?

Go to Tools → Table of Contents → Generate Table of Contents. Select which heading levels to include (H1, H2, H3). Sigil builds both the NAV document (EPUB 3) and NCX (EPUB 2 compatibility) from heading tags in all chapter files. Review the TOC in the right panel and drag to reorder if needed. Save with Ctrl+S.

How do I find and replace text across an entire EPUB in Sigil?

Open Find & Replace with Ctrl+H. In the scope dropdown, select 'All HTML Files' (not just 'Current File'). Enter your search term — Sigil supports full regex. Click 'Replace All' to apply across every chapter file in the EPUB at once. This is the fastest way to fix consistent formatting issues like wrong tag usage throughout a long book.

Sigil EPUB Editor — Complete Guide for Editing and Publishing EPUBs

Sigil is the best free open-source EPUB editor. It gives you direct access to every file inside an EPUB — HTML, CSS, images, fonts, and OPF metadata. Here's how to use it.

What Is Sigil?

Sigil (sigil-ebook.com) is a free, open-source EPUB editor for Windows, macOS, and Linux. It lets you:

Edit chapter HTML files directly (WYSIWYG or Code View)
Add, remove, and rename files inside the EPUB
Generate and edit the table of contents
Edit OPF metadata (title, author, language, ISBN)
Add and manage embedded fonts
Run Find & Replace across the entire EPUB
Validate with a built-in FlightCrew check

Sigil is the editor of choice for serious EPUB publishing. Calibre is better for conversion; Sigil is better for editing the result.

Installing Sigil

Windows: Download the installer from sigil-ebook.com. Requires Python 3 — Sigil's installer includes it.
macOS: Download the .dmg from sigil-ebook.com, or brew install --cask sigil.
Linux (Ubuntu/Debian): sudo apt install sigil. For newer versions, build from source or use the AppImage.

The Sigil Interface

Sigil has three main panels:

Book Browser (left): File tree showing all EPUB contents — Text/ (chapter XHTML files), Images/, Fonts/, Styles/ (CSS), Misc/ (OPF, NCX).
Editor (center): Opens files for editing. Switch between Book View (rendered) and Code View (raw HTML) with F2.
Table of Contents (right): Shows the current TOC structure with drag-to-reorder.

Core Editing Tasks

Edit Chapter Text

In the Book Browser, double-click a file under Text/ to open it.
Use Book View for WYSIWYG editing (bold, headings, lists with toolbar buttons).
Use Code View (F2) to edit raw HTML — useful for fixing structural issues.
Save with Ctrl+S.

Find and Replace Across the Whole EPUB

Sigil's Find & Replace (Ctrl+H) works across all files in the EPUB, not just the open file:

Open Find & Replace (Ctrl+H).
Check All HTML Files in the scope dropdown.
Enter search term (supports regex).
Click Replace All.

This is invaluable for fixing consistent formatting issues across a long book — replacing a mis-tagged paragraph style throughout all 50 chapter files at once.

Generate Table of Contents

Go to Tools → Table of Contents → Generate Table of Contents.
Select heading levels to include (H1, H2, H3).
Sigil builds the NAV document and NCX from headings in all chapter files.
Click OK. Review the TOC panel on the right.

Edit Metadata (Title, Author, Language, ISBN)

Go to Tools → Metadata Editor.
Edit Title, Author, Language (ISO code, e.g. "en"), and other Dublin Core fields.
Add an ISBN with Add Basic → select dc:identifier.
Click OK. Sigil updates the OPF file.

Add Images and Fonts

In the Book Browser, right-click Images/ (or Fonts/) → Add Existing Files.
Select your image or font file.
Sigil adds it to the manifest automatically.
Reference the image in HTML: <img src="../Images/photo.jpg" alt="Description"/>

Split a Chapter at the Cursor

To split one long chapter file into two:

Place the cursor where the split should occur.
Press Ctrl+Return (or Edit → Split at Cursor).
Sigil creates a new XHTML file at that point.

Validating Your EPUB in Sigil

Sigil includes FlightCrew for basic validation. For full EPUBCheck validation, run externally:

java -jar epubcheck.jar book.epub

Common Sigil-related warnings: generated files sometimes have unnecessary CSS attributes from older Sigil versions. These usually don't affect distribution but can be cleaned up.

Sigil vs Calibre Edit Book

Sigil: Purpose-built EPUB editor. Better code editing, regex search, TOC management, font obfuscation. Faster for text-heavy editing work.
Calibre Edit Book: Integrated into Calibre workflow. Better for quick fixes after conversion. Has built-in image compression. Requires Calibre to be installed.

Many publishers use both: Calibre for conversion and initial fixes, Sigil for detailed editing and final polish.

Converting a PDF to EPUB before editing in Sigil? toolkit.bot generates well-structured EPUB output.

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