OpenWords is a free multilingual vocabulary learning app, currently available for English, Dutch, Polish, and Russian learners — built by an indie team of three based in the Netherlands.
The project started in September 2025, when the three of us kept hitting the same wall while learning a foreign language: remembering new words. Vocabulary is by far the most time-consuming part of that journey, and we needed a way to learn words efficiently and retain them long-term.
To solve the frustration of forgetting a new word the day after you learn it — and to give people a tool that beats the forgetting curve.
The deeper frustration is that existing solutions fall short: shallow one-word translations with no context, no way to form solid associations, and annoying ads or paywalls.
Good vocabulary learning needs rich context — clear definitions, natural example sentences, and the nuances of how a word is actually used.
AI is now genuinely good with language, so with the right tools a small team can take on complex linguistic tasks at scale — cleaning, structuring, and enriching dictionary data into entries with real depth.
We build OpenWords on Wiktionary as our source dictionary — the free and remarkable work of many linguists. We parse it with kaikki, use AI to clean and enrich the data, and apply the FSRS algorithm used in Anki for scheduling.
The result is a rich dictionary entry for every word: all its meanings, examples, CEFR level, synonyms, and common phrases. Save a meaning in one tap, and multi-format flashcards are generated automatically and scheduled for review. No setup, all context — just learn.
True to its name, OpenWords is free for everyone to use.
OpenWords builds on open language data and open-source tools. Our dictionary content comes from Wiktionary, parsed with kaikki/wiktextract, and is licensed under CC BY-SA 4.0. For spaced repetition we use a Kotlin port, FSRS-Kotlin, under the MIT License — originally developed by Jarrett Ye with the Open Spaced Repetition community.
Our own application source code is released under the Business Source License 1.1. It is free to use for personal, educational, research, and non-profit purposes, and converts to GPL 3.0 over time.
16+ years in software development, focused on large-scale systems and data infrastructure
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