Our verdict: Sigil is the standard free tool for building and fixing EPUB files by hand. It gives full control over the HTML and CSS inside a book, which is exactly what self-publishers and ebook editors need, but beginners who just want to write a book will find it technical.
About Sigil
Sigil is an editor for EPUB ebooks, maintained by volunteers and released under the GNU GPL v3. It opens an EPUB as a set of files: XHTML chapters, style sheets, images and fonts. You edit them in Code View with direct access to the markup, or check the result in Preview, and Sigil packages everything back into a valid EPUB 2 or EPUB 3 file.
Tools include a table of contents generator with multi-level headings, a metadata editor, spell checking with custom dictionaries, and find and replace with full PCRE regular expressions across all files. Checkpoints save snapshots you can compare later, and Python plugins add extra functions such as validation or format conversion. Sigil imports EPUB and HTML files, images and style sheets.
What it does well
- Code and preview. Edit XHTML and CSS directly and see the rendered page side by side.
- EPUB 2 and 3. Creates and edits books in both EPUB versions.
- Table of contents. Generates a multi-level TOC from the headings in your chapters.
- Regex find and replace. PCRE search and replace across every file in the book.
- Plugins and checkpoints. Extend Sigil with Python plugins and compare saved snapshots.
Who it is for
Good fit
Self-publishers, ebook formatters and editors who want precise control over EPUB markup.
Look elsewhere
Writers looking for a word processor, or anyone who needs Kindle KPF or PDF output.
Pros and cons
Pros
- Free and open source
- Full control over EPUB HTML and CSS
- Powerful regex search across the whole book
- Plugin system
Cons
- Requires basic HTML and CSS knowledge
- Edits only EPUB; no direct Kindle or PDF export
- Windows build is x64 only and needs Windows 10 1809 or newer
How to install Sigil
The download button fetches the Windows x64 installer from the official Sigil GitHub release, the same file linked on sigil-ebook.com. Windows SmartScreen may warn about the publisher; the site notes that winget and Chocolatey install the same unmodified installer. Python plugins are installed later from Plugins > Manage Plugins.
Questions about Sigil
Is Sigil free?
Yes. Sigil is free and open source under the GNU GPL v3 and is developed by volunteers.
Does Sigil support EPUB 3?
Yes. Sigil creates and edits both EPUB 2 and EPUB 3 books.
Can Sigil convert Word documents to EPUB?
Not directly. Sigil imports EPUB and HTML files, so save the document as HTML first or use a converter such as Calibre.
