Credits & licenses

Word Skyline writes its own learner definitions, example sentences and questions. To choose which words to teach and to check meanings, we use the open resources below. Their authors do not endorse this product.

Word lists

New General Service List 1.2 and New Academic Word List 1.2 by Browne, C., Culligan, B., and Phillips, J., https://www.newgeneralservicelist.com, licensed under CC BY-SA 4.0.

Changes: we combined both lists, filtered them by study topic and frequency, and added columns linking each word to a meaning. Our derived selection list is shared under the same license: Academic English Starter selection (CSV).

TOEIC Service List 1.2 by Browne, C. and Culligan, B. https://www.newgeneralservicelist.com/toeic-service-list, licensed under CC BY-SA 4.0.

Changes: selected TSL words by rank, grouped them for work and travel, and added word classes and available CEFR-J levels. This adapted list is shared under CC BY-SA 4.0. Workplace English selection (CSV).

The CEFR-J Wordlist Version 1.6. Compiled by Yukio Tono, Tokyo University of Foreign Studies. Retrieved from https://cefr-j.org/download.html on October 20, 2026. We use its word levels only as a reference when choosing words; they are not official levels for individual meanings.

Spanish word list

wordfreq 3.2 by Robyn Speer, https://github.com/rspeer/wordfreq, licensed under CC BY-SA 4.0. It contains data from Google Books Ngrams, the Leeds Internet Corpus, Wikipedia, ParaCrawl, OPUS OpenSubtitles 2018 (http://www.opensubtitles.org/), the SUBTLEX word lists by Marc Brysbaert et al. (freely available data), and the Twitter streaming API.

We use its Spanish word frequencies only to choose and order the words of the Spanish Starter pack. The meanings and example sentences are our own.

Japanese word list

wordfreq 3.2 by Robyn Speer, https://github.com/rspeer/wordfreq, licensed under CC BY-SA 4.0. It contains data from OPUS OpenSubtitles 2018 (http://www.opensubtitles.org/), Wikipedia, ParaCrawl, the Leeds Internet Corpus, Google Books Ngrams and the SUBTLEX word lists by Marc Brysbaert et al. (freely available data).

We use its Japanese word frequencies only to choose and order the words of the Japanese Starter pack. The meanings and example sentences are our own.

This product uses the JMdict dictionary files, which are the property of the Electronic Dictionary Research and Development Group and are used in conformance with the Group’s licence: https://www.edrdg.org/edrdg/licence.html. JMdict, licensed under CC BY-SA 4.0.

We use JMdict only to choose words and to check their readings and parts of speech. The meanings and example sentences are our own.

French word list

wordfreq 3.2 by Robyn Speer, https://github.com/rspeer/wordfreq, licensed under CC BY-SA 4.0. It contains data from OPUS OpenSubtitles 2018 (attribution to OpenSubtitles, http://www.opensubtitles.org/), Wikipedia, ParaCrawl, the Leeds Internet Corpus, Google Books Ngrams and SUBTLEX word lists by Marc Brysbaert et al.

We use its French word frequencies only to choose and order the words of the French Starter pack. The meanings and example sentences are our own.

Lexique 4.10 by Boris New, Christophe Pallier and contributors, http://www.lexique.org, licensed under CC BY-SA 4.0. New, B., Pallier, C., Schalchli, G., Bourgin, J. and Gimenes, M. (2026), Lexique 4: A major upgrade of the "Lexique" French lexical database, Behavior Research Methods, 58(5), 140.

We use Lexique only to check lemmas, noun genders and verb forms. The course contains no Lexique data.

Dictionary data

Open English WordNet 2025 by the Open English WordNet team, https://en-word.net, licensed under CC BY 4.0, based on Princeton WordNet. We use it to identify meanings while editing; we do not copy its definitions.

License notice (original English)

This software and database is being provided to you, the LICENSEE, by the Open English Wordnet team under the Creative Commons Attribution 4.0 International License (CC-BY 4.0).

Permission to use, copy, modify and distribute this software and database and its documentation for any purpose and without fee or royalty is hereby granted, provided that you agree to comply with the following copyright notice and statements, including the disclaimer, and that the same appear on ALL copies of the software, database and documentation, including modifications that you make for internal use or for distribution.

THIS SOFTWARE AND DATABASE IS PROVIDED "AS IS" AND PRINCETON UNIVERSITY MAKES NO REPRESENTATIONS OR WARRANTIES, EXPRESS OR IMPLIED. BY WAY OF EXAMPLE, BUT NOT LIMITATION, PRINCETON UNIVERSITY MAKES NO REPRESENTATIONS OR WARRANTIES OF MERCHANTABILITY OR FITNESS FOR ANY PARTICULAR PURPOSE OR THAT THE USE OF THE LICENSED SOFTWARE, DATABASE OR DOCUMENTATION WILL NOT INFRINGE ANY THIRD PARTY PATENTS, COPYRIGHTS, TRADEMARKS OR OTHER RIGHTS.

The name of Princeton University or Princeton may not be used in advertising or publicity pertaining to distribution of the software and/or database. Title to copyright in this software, database and any associated documentation shall at all times remain with Princeton University and LICENSEE agrees to preserve same.

Software

Spaced review uses ts-fsrs (MIT). The 3D skyline uses three.js (MIT). The site is built with React, Hono and Zod (MIT licenses).

Fonts

Bricolage Grotesque and Atkinson Hyperlegible Next, both under the SIL Open Font License 1.1, served from this site.

Scene and sound

The islands, tower and bridge are built from simple shapes in code for this project. Sound effects are synthesized in your browser. The words, the example sentences and the narration in the “how to play” demos are spoken by Kokoro-82M (Apache License 2.0), generated for this project.

French recordings use its ff_siwis voice.

Kokoro v1.0 was trained in part on the CC BY audio below. The recordings in every language come from this model.

Koniwa (声庭), tnc series: readings by announcers of Television Nishinippon, licensed under CC BY 3.0.
Yamagishi, Junichi; Honnet, Pierre-Edouard; Garner, Philip; Lazaridis, Alexandros. (2017). The SIWIS French Speech Synthesis Database, 2016 [dataset]. University of Edinburgh. School of Informatics. The Centre for Speech Technology Research. https://doi.org/10.7488/ds/1705, licensed under CC BY 4.0.

Changes: our recordings are newly synthesized speech, not audio from either dataset.

Trademarks

IELTS, TOEFL, PTE and TOEIC are trademarks of their respective owners. This product is not affiliated with, or endorsed by, any exam provider, including ETS. Our word packs are not official exam lists, and we do not promise a score.

DELE is a trademark of its owner. This product is not affiliated with, or endorsed by, the Instituto Cervantes or any other exam provider. Our Spanish word packs are not official exam lists, and we do not promise a result.

The Japanese-Language Proficiency Test (JLPT) is run by The Japan Foundation and Japan Educational Exchanges and Services. This product is not affiliated with, or endorsed by, them or any other exam provider. Our Japanese word packs are not official exam lists, and we do not promise a result.

DELF is an official French diploma awarded by the Ministry of National Education and designed and run by France Éducation international. This product is not affiliated with, or endorsed by, them or any other exam provider. Our French word packs are not official exam lists, and we do not promise a result.