Calibre review

Calibre is best known as an ebook library manager, but it also gives authors two useful production tools for free. The converter turns personal documents and dozens of file types into ebooks and can create a table of contents, adjust styles and fix punctuation along the way. The integrated editor opens EPUB, KEPUB and AZW3 files and shows the HTML and CSS inside, with a live preview that updates as you type. Automated tools cover the jobs that trip up self-publishers: Check Book finds errors, and there are tools to embed and subset fonts, remove unused CSS, insert an inline table of contents and make the book more accessible. Calibre runs on Windows, macOS and Linux, and a portable build runs from a USB stick. The cost of all that power is approachability. There are no designed templates, and fixing a book means reading markup. Authors who want a guided layout should use Reedsy Studio or Atticus and keep Calibre for conversion and cleanup.

Who it is for

Technical authors and publishers who want free conversion between formats and direct editing of ebook HTML and CSS.

Price

Free and open source; optional donations.

It’s also completely free and open source and great for both casual users and computer experts.
Quoted from the vendor pricing page on November 11, 2026.

Key features

• Converts dozens of file types and can build a table of contents
• Integrated editor for EPUB, KEPUB (Kobo) and AZW3 (Kindle) books
• Live preview that updates as you edit HTML and CSS
• Check Book tool, font embedding and subsetting, and accessibility tools
• Metadata editing and a built-in ebook viewer

Strengths and weaknesses

• Strength: Completely free and open source
• Strength: Runs on Windows, macOS and Linux, with a portable version
• Strength: One app for converting, editing, checking and reading ebooks
• Weakness: Editing happens in HTML and CSS, which suits technical users more than beginners
• Weakness: No guided book design themes like Vellum or Atticus
• Weakness: The interface is built around library management rather than writing

Key facts

• Price: Free, open source
• Platforms: Windows, macOS, Linux, portable
• Editable formats: EPUB, KEPUB, AZW3
• Developer: Kovid Goyal and contributors

Where it ranks

Calibre is No. 4 in our Best Ebook Creation Software verdict.