Japanese dictionary data
Nikki’s word lookups are built on dictionary files from the Electronic Dictionary Research and Development Group (EDRDG) at Monash University. We are grateful for their work, which has underpinned Japanese-language software for decades.
- JMdict/EDICT — the Japanese-English dictionary behind word lookups and definitions. Copyright © Electronic Dictionary Research and Development Group. Used under Creative Commons Attribution-ShareAlike 4.0. Modified: the data has been converted and restructured into this application’s own format.
- KANJIDIC2 — kanji readings, meanings and frequency rankings. Copyright © Electronic Dictionary Research and Development Group. Used under Creative Commons Attribution-ShareAlike 4.0. Modified: selected fields have been extracted and restructured into this application’s own format.
The full licence statement for these files is published by EDRDG at edrdg.org/edrdg/licence.html, and the licence itself at creativecommons.org/licenses/by-sa/4.0.
Kanji stroke data
Nikki’s kanji writing practice is built on KanjiVG, an open dataset of kanji stroke shapes and stroke order created by Ulrich Apel and the KanjiVG project. We are grateful for this work, which is what makes learning to write kanji possible here.
- KanjiVG — per-kanji stroke paths and stroke order, at kanjivg.tagaini.net. Copyright © Ulrich Apel and the KanjiVG project. Used under Creative Commons Attribution-ShareAlike 3.0. Modified: each character’s strokes have been converted into this application’s own JSON, with sampled centre-line points added so a learner’s tracing can be graded.
KanjiVG is licensed under CC BY-SA 3.0, a different version from the dictionary data above. The stroke data Nikki serves is an adaptation of KanjiVG, so under ShareAlike it is offered under the same licence. As with the dictionary data, the licence attaches to that stroke data alone — not to the Nikki AI application, its source code, or its other content.
Word frequency data
Nikki teaches the most common words first. The order comes from wordfreq, a collection of word frequencies in many languages created by Robyn Speer.
- wordfreq — how often each Japanese word is used, at github.com/rspeer/wordfreq. Copyright © Robyn Speer. Used under Creative Commons Attribution-ShareAlike 4.0. Modified: the frequencies have been turned into a ranking of the words in Nikki’s study lists.
Pitch accent data
The pitch diagrams on word cards come from UniDic, a dictionary of Japanese made by the National Institute for Japanese Language and Linguistics (NINJAL).
- UniDic (version 2025.12) — the pitch accent of each word, at clrd.ninjal.ac.jp/unidic. Copyright © 2023 National Institute for Japanese Language and Linguistics. Used under the BSD licence below. Modified: only the accent of each word is used, matched to the words in Nikki’s dictionary and study lists.
Copyright (c) 2023 National Institute for Japanese Language and Linguistics
Redistribution and use in source and binary forms, with or without modification, are permitted provided that the following conditions are met:
* Redistributions of source code must retain the above copyright notice, this list of conditions and the following disclaimer.
* Redistributions in binary form must reproduce the above copyright notice, this list of conditions and the following disclaimer in the documentation and/or other materials provided with the distribution.
* Neither the name of the UniDic Consortium nor the names of its contributors may be used to endorse or promote products derived from this software without specific prior written permission.
THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
Reusing our dictionary data
The ShareAlike half of that licence asks that an adapted copy of the data be offered on the same terms. Our English-to-Japanese dictionary file is such an adaptation and is downloaded in full by the app, so we offer it under the same licence:
- eng-jp-dict.json — derived from JMdict, made available under Creative Commons Attribution-ShareAlike 4.0. Its notice and terms sit beside it at eng-jp-dict.LICENSE.txt.
To be clear about what that covers: the licence applies to that file and the dictionary data inside it. It does not apply to the Nikki AI application, its source code, its lessons, or anything else it stores — ShareAlike attaches to the adapted data, not to software that reads it.
Corrections
If you believe something here is incomplete or a source has been credited incorrectly, please tell us — attribution errors are worth fixing quickly, and we would rather hear about one than leave it standing. You can reach us from the Support page.