Why the word set matters
At the beginning, reading an unfamiliar Japanese passage can turn into a long series of dictionary lookups. Knowing most of the vocabulary frees your attention for the sentence and its meaning. This reader looks for a complete prepared story whose words fit the set you selected. Every token in both the Japanese title and the story is checked before it appears. If a word is outside that set, the story does not pass.
What “your words” means here
Choosing a vocabulary word permits its inflected forms in this library. For example, knowing 食べる can permit 食べ in a polite sentence. Particles, endings and names are separate permissions. The checked option above adds a specific, reviewable list of them, including は, です and the character names ユキ and ケン. Those additions are part of the effective word set, not words the tool assumes you already know. Uncheck the option if you want to supply those forms individually.
How to read a matched story
Read it once without stopping, even if you move slowly. Then read it aloud. Tap a word for its meaning when you need help. The English translation starts closed, so you can decide when to consult it. Try hiding furigana for a second pass and notice which kanji you recognise in context. There is no score or deadline: the point is to follow the story with as little interruption as possible.
Presets and pasted lists
The Niwa preset contains the app’s 502 core words. It is not an official N5 syllabus. N5 and Genki lesson presets are shown as unavailable because verified membership data is not bundled yet. For your own list, enter one word per line in kana or kanji. The tool identifies words within the core library. If a kana spelling could refer to several words, it asks you to choose a meaning instead of quietly granting every homophone. Unsupported entries are reported so you can revise them.
Why a list might have no story
This tool matches whole, prepared Niwa stories; it does not ask a language model to invent one during your visit. A small or unusual list may not fit any complete story. In that case you get an explanation rather than a passage with extra vocabulary slipped in. The reader aims for three to five sentences with smaller sets and six to eight with larger ones, but a shorter complete story is preferable to one that breaks your constraint. The sample list provides a small set with a matching story.
What this can and cannot show
Recognising the words does not guarantee that you know every grammar pattern or understand the passage immediately. Short stories also repeat familiar ideas, and a finite library cannot accommodate every possible vocabulary list. Nation’s 2006 discussion of high known-word coverage concerns English reading; it provides useful context, not a measured Japanese threshold or a guarantee about this tool. Keep the list growing at your own pace, and use translations and lookups as support when they help.
Source: complete prepared stories and reviewed words from Niwa’s v8 library. JMdict-derived word data is shared under CC BY-SA 4.0, EDRDG. The selected data and provenance include the tool’s vocabulary and matched-story pool.