Joseph Conrad · 1857
Heavy going at CET-4 level. Not unreadable — just not readable the look-every-word-up way.
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 128 of them.
Advanced — read it with glosses. 38,515 words in total; at 150 words a minute for a non-native reader, about 4 h 17 min to finish. Average sentence length 15.4 words. This book is heavy on rare, archaic and invented words: even 25,000 high-frequency word families will not reach 95% coverage — its difficulty is not in the common vocabulary.
The opening of Heart of Darkness, 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.
had then, as you remember, just returned to London after a lot of Indian Ocean, Pacific, China Seas—a regular dose of the East—six years or so, and I was loafing about, hindering you fellows in your work and invading your homes, just as though I had got a heavenly mission to civilize you. It was very fine for a time, but after a bit I did get tired of resting. Then I began to look for a ship—I should think the hardest work on earth. But the ships wouldn’t even look at me. And I got tired of that game, too.
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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 measured against the CET-4 ∪ Gaokao lists, so this is difficulty for a Chinese-speaking learner, not a native-child reading level.