License information
Jankobo is distributed under noncommercial, non-profit licenses. The source code and the art and sound follow two different licenses, but neither allows commercial use. This page is a plain-language summary and does not replace the license texts; where the two seem to differ, follow the license text.
At a glance
- You can: use, change and share the code, art and sound for any noncommercial purpose, such as personal study, hobby projects, research or teaching.
- You must: pass on the license and the copyright notice when you share, and credit the source of the art and sound and say if you changed them.
- You cannot: use the code, art or sound for commercial purposes, such as selling them or building them into a paid service.
Source code: PolyForm Noncommercial License 1.0.0
All of this project's source code, from the mahjong rules engine and the bots to the web app, the friend room server and the build scripts, follows the PolyForm Noncommercial License 1.0.0. The only exception is the art and sound described below.
- Allowed: use, change and distribute it for any noncommercial purpose. The license names personal research, study, private entertainment and hobby projects as examples, and also counts use by charitable organizations, educational institutions, public research organizations, government institutions and the like as a permitted purpose.
- Condition: anyone who gets a copy from you must also get the license text (or its URL) and the copyright line that begins with "Required Notice:".
- Not allowed: commercial use.
- Patents: the license includes a patent license. It ends immediately if you make a written claim that the software infringes a patent.
- No warranty: as far as the law allows, the software comes as is, without any warranty.
- What it is: a source-available license, not an OSI-approved open source license, because no OSI-approved license restricts commercial use.
Required Notice: Copyright 2026 jankobo - ippatsu (https://github.com/jankobo/ippatsu)
Full text of the PolyForm Noncommercial License 1.0.0
Art and sound: CC BY-NC 4.0
The art and sound in the game (tile faces, table and region art, character art, sound effects, music and voices), and the tile and table art made by the project's generation scripts, are licensed under Creative Commons Attribution-NonCommercial 4.0 International (CC BY-NC 4.0).
- Share: copy and redistribute the material in any medium or format.
- Adapt: remix, transform and build upon the material.
- Attribution: credit the source (jankobo / ippatsu), link to the license and say if you made changes. Do not suggest that the creator endorses you or your use.
- NonCommercial: do not use the material for commercial purposes.
- No additional restrictions: do not add legal terms or technological measures that stop others from doing anything the license permits.
Read the CC BY-NC 4.0 summary (Creative Commons)
An attribution line can look like this:
Art: jankobo / ippatsu (https://github.com/jankobo/ippatsu), CC BY-NC 4.0 (https://creativecommons.org/licenses/by-nc/4.0/), colors changed from the original
Full legal code of CC BY-NC 4.0
The bundled fonts are not covered by this license. Space Grotesk, and Ippatsu Sans KR and JP (subsets of IBM Plex Sans KR and JP cut down to the characters this app uses, then renamed), each keep their original SIL Open Font License 1.1.
Full license text of the IBM Plex fonts
Resources made with AI
Some of the illustrations, voices and background music were made with generative AI services. For example, OpenAI's image generation model (gpt-image) was used for pictures and ElevenLabs for the character voices.
The CC BY-NC 4.0 grant above covers the rights jankobo holds. When you reuse these resources, the terms of service of the service that made them may apply as well.
Third-party software
Jankobo also includes software and fonts made by others: kobalab's mahjong engine (@kobalab/majiang-core 1.4.1 and @kobalab/majiang-ai 1.1.0, MIT License, Copyright (c) 2021 Satoshi Kobayashi), the grading basis for the What Would You Discard? problems; three.js (MIT License), which draws the table; small runtime pieces that the build tools Vite and Rolldown insert (MIT License); and the fonts above. Their full license texts are collected in the notice file below.
Third-party notices (THIRD-PARTY-NOTICES.txt)
Your own themes and profile
Pictures, names and lines you add to a custom theme or your profile are not Jankobo's art or sound, so these licenses do not cover them. The rights belong to whoever made them (you, if you made them yourself), and you are responsible for registering and using them. In the app, the Your responsibility note next to the theme save button and in the My Profile window explains this in detail.
Your themes and profile are saved on this device. A portrait you pick as your face in a friend room, and the host's theme in a room with Shared look turned on, are uploaded to the server so the people in that room can see them.
Copyright notice
Copyright 2026 jankobo - ippatsu. When you reuse the code, art or sound, credit jankobo / ippatsu and link to the repository (https://github.com/jankobo/ippatsu).
Contact
For questions about the licenses or commercial use, write to find1086@gmail.com. It is the same address as the contact on the in-game Patch Note screen.
The repository (https://github.com/jankobo/ippatsu) is currently private. To view the source or ask anything else, contact the address above.