head to head · open source
calibre-web vs substance
calibre-web has 18,530 GitHub stars, 1,902 forks, 409 open issues and last shipped 26 days ago. substance has 2,737 stars, 121 forks, 41 open issues and last shipped 7 months ago. calibre-web leads on adoption by 577% (18,530 vs 2,737 stars). calibre-web is written in Fluent under GPL-3.0; substance is written in JavaScript under MIT. calibre-web has attracted 10% as many forks as stars, substance 4%. calibre-web was the more recently maintained of the two, and both are self-hostable with no licence fee.
Two open source projects, one decision. Both are free and self-hostable — the differences are community size, license terms, language stack and release pace.
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Side by side
| calibre-web | substance | |
|---|---|---|
| GitHub stars | ★ 19K | ★ 2.7K |
| License | GPL-3.0 | MIT |
| Written in | Fluent | JavaScript |
| Last push | 2026-10-10 | 2026-04-02 |
| Forks | ⑂ 1.9K | ⑂ 121 |
| Self-hosting | Yes | Yes |
| Data ownership | Your server | Your server |
pick calibre-web if
- You weight community size — 19K stars and counting
- You want the GPL-3.0 license terms
- Your stack matches Fluent
- You value the larger contributor base for long-term maintenance
pick substance if
- You want the substance feature set and don't need the biggest community
- You prefer the MIT license terms
- Your stack matches JavaScript
- You evaluated both and substance fits your workflow better
About calibre-web
Calibre Web Calibre Web is a web app that offers a clean and intuitive interface for browsing, reading, and downloading eBooks using a valid Calibre database. Table of Contents (click to expand) 1. About 2. Features 3. Installation Installation via pip (recommended) Quick start Requirements 4. Docker Images 5. Troubleshooting 6. Contributor Recognition 7. Contact 8. Contributing to Calibre Web This software is a fork of library and licensed under the GPL v3 License. Features Modern and responsive Bootstrap 3 HTML5 interface Full graphical setup Comprehensive user management with fine grained per user permissions…
read the full calibre-web overview →
About substance
Substance.js Substance is a JavaScript library for web based content editing. It provides building blocks for realizing custom text editors and web based publishing system. It is developed to power our online editing platform Substance. Development Install the dev dependencies. Run the dev server. Navigate to for the running the browser test suite. The test suite is rebuilt as you make changes to the source files. To run the test suite headless.
read the full substance overview →
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Frequently asked questions
Is calibre-web or substance more popular?
calibre-web has 18,530 GitHub stars and substance has 2,737. calibre-web has the larger community by that measure.
Are calibre-web and substance free?
Both are open source. calibre-web is licensed under GPL-3.0 and substance under MIT. Neither carries a licence fee.
What is the difference between calibre-web and substance?
calibre-web is written in Fluent and substance in JavaScript. The practical differences are community size, licence terms, language stack and release cadence — all compared in the table above.
Which should I choose, calibre-web or substance?
Choose calibre-web if you want the larger community (18,530 stars) or its GPL-3.0 licence terms. Choose substance if its feature set, stack or MIT licence fits better. Both are self-hostable.