head to head · open source
koreader vs substance
koreader has 29,761 GitHub stars, 1,908 forks, 1,345 open issues and last shipped yesterday. substance has 2,733 stars, 121 forks, 41 open issues and last shipped 6 months ago. koreader leads on adoption by 989% (29,761 vs 2,733 stars). koreader is written in Lua under AGPL-3.0; substance is written in JavaScript under MIT. koreader has attracted 6% as many forks as stars, substance 4%. koreader 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
| koreader | substance | |
|---|---|---|
| GitHub stars | ★ 30K | ★ 2.7K |
| License | AGPL-3.0 | MIT |
| Written in | Lua | JavaScript |
| Last push | 2026-09-17 | 2026-04-02 |
| Forks | ⑂ 1.9K | ⑂ 121 |
| Self-hosting | Yes | Yes |
| Data ownership | Your server | Your server |
pick koreader if
- You weight community size — 30K stars and counting
- You want the AGPL-3.0 license terms
- Your stack matches Lua
- 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 koreader
KOReader is a free, AGPL 3.0 licensed document viewer written in Lua that runs on e ink readers from Cervantes, Kindle, Kobo and PocketBook, on reMarkable, and on Android and desktop Linux, aimed at readers who want broader format support, finer typesetting control and better performance than the reading software shipped with their device.
read the full koreader overview →
About substance
Substance is a JavaScript library for web based content editing. It lives in the JavaScript and Content & Publishing / Publishing ecosystem, and it is distributed under the MIT license. The README describes it as a library that provides building blocks for realizing custom text editors and web based publishing systems, and it was developed to power the online editing platform Substance.
read the full substance overview →
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Frequently asked questions
Is koreader or substance more popular?
koreader has 29,761 GitHub stars and substance has 2,733. koreader has the larger community by that measure.
Are koreader and substance free?
Both are open source. koreader is licensed under AGPL-3.0 and substance under MIT. Neither carries a licence fee.
What is the difference between koreader and substance?
koreader is written in Lua 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, koreader or substance?
Choose koreader if you want the larger community (29,761 stars) or its AGPL-3.0 licence terms. Choose substance if its feature set, stack or MIT licence fits better. Both are self-hostable.