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).

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.

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.

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).

Open English Wordnet 2023 Copyright 2023 by the Open English Wordnet team.

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.

WordNet 3.1 Copyright 2011 by Princeton University. All rights reserved.

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.

Trademarks

IELTS, TOEFL, PTE and Duolingo English Test are trademarks of their respective owners. Word Skyline is not affiliated with, or endorsed by, any exam provider, and our word packs are not official exam lists.