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Sigil vs Standard Ebooks Toolset: catalog facts
Sigil	Standard Ebooks Toolset
Free Free and open source under the GPL.	Free Free and open source.
Windows, macOS, Linux	macOS, Linux, Command line
Edits EPUB 2 and EPUB 3 in a visual view or directly in the XHTML Built-in validation catches the errors that make readers reject a book	Lints ebook source against a detailed style guide Builds finished EPUB files
EPUB only; it does not handle MOBI, AZW3 or PDF Some XHTML and CSS knowledge is needed to fix anything non-trivial	Command line only Built around the Standard Ebooks conventions
Downloadable app	Downloadable app
Open source	Open source
License: GPL-3.0	License: GPL-3.0
No account needed	No account needed
Works offline	Works offline
Official website Full listing and sources Checked September 21, 2026	Official website Full listing and sources Checked October 2, 2026

Catalog facts only. Anything “not stated” is unconfirmed. Check full listings for details.