Sigil

What Sigil is for

Sigil is an editor for the inside of an EPUB. Where a word processor shows you a page, Sigil shows you the book as it is actually packaged: a set of XHTML documents, a stylesheet or two, images, fonts, a manifest and a spine. You edit those files directly, with syntax highlighting for XHTML and CSS, and a preview pane renders the result as a reader would see it. Both EPUB 2 and EPUB 3 are supported, including EPUB 3 navigation documents, fixed-layout metadata and Media Overlays. The project describes itself as a multi-platform ebook editor built to edit books in EPUB format, and that narrowness is the point: nothing here is trying to be a word processor.

The editing workflow

A typical pass through a book is mechanical rather than artistic. You open the EPUB, fix the metadata record, then work through the text: Mend and Prettify normalises indentation and closes loose tags, Find & Replace runs plain or regular-expression searches across the whole book or a chosen file group, and Clips paste frequently used markup fragments. The Book Browser keeps every file in a folder tree, so stylesheets, images and fonts are edited in place instead of being re-imported. Reports list images, stylesheets, links, characters and files with their sizes, which is how you spot a stray 4 MB cover before publishing. A table-of-contents editor and a footnote tool handle the two structural jobs that are tedious by hand, and Checkpoints preserve a snapshot you can return to when an ambitious find-and-replace goes wrong.

Practical limits and configuration

Sigil is deliberately not WYSIWYG: the current 2.x line leads with the code view and a read-only preview, so comfortable use assumes a working grasp of XHTML and CSS. Validation matters more than it sounds. The app bundles the EPUB checker and surfaces its errors in a panel, which is the fastest way to catch a malformed OPF or a missing manifest entry; run it before every export because readers are unforgiving about structure. Plugins extend the editor through Python, and the community index includes import and cleanup tools, but plugin quality varies. Spell checking works through installed dictionaries. Sigil has no PDF or DOCX export and no page-layout features, and it edits one book at a time with no collaboration layer; for those you convert with another tool or hand the manuscript to a layout program.

Who should choose something else

If you write in a word processor and want an ebook out of it, start there and convert with calibre, then come back to Sigil only if the result needs surgery. If you want to design print pages, a desktop publishing program is the right tool. If you prefer a visual, template-driven builder with no markup, a hosted ebook service will be quicker. Choose Sigil when you care about a validated, hand-controlled EPUB and are willing to work in the source.