Think of a text editor in the lines of Word or Writer that allows you to create EPUB books using a WYSIWYG approach. An EPUB editor complete with icons to add headings and change your fonts with one click, with multimedia support, a Table of Contents generator, a spell checker, and an EPUB validation tool. That is what Sigil is all about – an open-source e-book creation and editing tool for both professional and amateur EPUB publishing.
Though it may help you to fine-tune your EPUB books, you don’t need to be an HTML expert to use Sigil. The program offers you the possibility of writing directly on the HTML code and see the changes in real time in the program’s preview window, and vice versa. Despite its overall ease of use and its useful validation tool, Sigil still requires a certain learning curve if you want to become a professional EPUB publisher using this app. It's excellent EPUB guide, however, will help you reach the required level of excellence.
Internally, EPUB books are a set of W3C-compliant files that provide your e-book with a level of navigability that you won’t find in, for instance, PDF files. Its multimedia support allows you to include (JPEG, PNG, GIF, and even SVG) images, (MP3, AAC, MPEG, and M4A) audio files, (MP4, Ogg, WebM, and M4V) videos, and, of course, text in the form of HTML and XML files. An NCX file stores the navigable structure of the book, i.e., its table of contents. An EPUB container (which is, in fact, a ZIP file) can include as many files as you wish, and Sigil allows you to “cut” your book into logical units (parts, chapters, subchapters, etc.) and to link the text to all other files that are part of it.
Sigil allows you to write your EPUB books from scratch, and apply to the text a variety of features similar to those your standard word processor offers you. Bold, italics, underlined text, different fonts, indentations, lists, Unicode symbols, and – of course – HTML headings, CSS stylesheets, and other labels are all supported. Alternatively, you can load a TXT or HTML file and transform it into full-featured EPUB books in minutes – add chapter breaks, headings, links, and whatever other elements are required to transform a lame text file into a navigable, fully-structured EPUB e-book. Finally, you can also load an existing EPUB book and perform as many edits and changes as required and check them in real time, add images and multimedia files to it, a cover image and all the required metadata, or simply validate that the EPUB structure is consistent with the W3C rules. Though the current EPUB validator used by Sigil (FlightCrew) is superior in every way to the old Tidy from earlier versions, it’s still not 100% accurate – according to Sigil’s developers – and that is why you’re advised to check your book externally using EpubCheck, especially if your e-book’s level of complexity is fairly high.
Thanks to Sigil and its constant renovation, creating truly professional and fully-compliant EPUB books in an intuitive way is no longer exclusive to publishers. You can now self-publish your own books in what has become the de facto standard for the e-book publishing industry using an open-source tool designed by e-book users for e-book users.