Johanna Spyri · 1881
Reads steadily at a 5,000-word vocabulary. An unknown word here and there, usually carried by the sentence around it.
Coverage = the share of words in the text you already know. The research gives two lines: 98% before independent fluent reading is realistic, 95% for the instructional level that needs support (Hu & Nation, 2000). Proper nouns are not counted as unknown — recognising that it is a name is enough; this book has 167 of them.
Finishable at 5,000 words, with the odd lookup. 91,721 words in total; at 150 words a minute for a non-native reader, about 10 h 11 min to finish. Average sentence length 23.1 words — on the long side, so the load comes from sentence structure as much as from vocabulary. Reaching 95% coverage on this book (the floor for readability) takes roughly 5,250 word families.
The opening of Heidi, word for word. Tap any word you don't know and its meaning here appears beside it — no sign-up, tap as often as you like.
From the old and pleasantly situated village of Mayenfeld, a footpath winds through green and shady meadows to the foot of the mountains, which on this side look down from their stern and lofty heights upon the valley below. The land grows gradually wilder as the path ascends, and the climber has not gone far before he begins to inhale the fragrance of the short grass and sturdy mountain-plants, for the way is steep and leads directly up to the summits above.
On a clear sunny morning in June two figures might be seen climbing the narrow mountain path; one, a tall strong-looking girl, the other a child whom she was leading by the hand, and whose little checks were so aglow with heat that the crimson color could be seen even through the dark, sunburnt skin.
👆 Tap any word to try it
Readii cuts this book into three-minute passages. Tap a word you don't know and its meaning in that exact sentence appears in place — no jumping out, no losing the thread.
The opening chapters are free — no account, no card.
Ordered by unknown words per 100. Lower reads easier; to step up a level, pick a higher number.
Computed by Readii from the public-domain text (updated 2026-10-21), not estimated by hand. The Readii reading level is our own scale, anchored on unknown-word density; it is not the same system as Lexile or AR and does not convert directly. Unknown words are counted against a frequency list built from a large subtitle corpus, so the bands mean the same thing for any learner of English, whatever your first language. This is difficulty for a non-native reader, not a native-child reading level.