Required for AI writing grader (写作 mode). Stored only in your browser's localStorage.
An integrated Chinese study system — from foundations (214 Kangxi radicals, 5,000 HSK words, 75 measure words with paired nouns) up to research-level training (academic reading, cloze, spaced-repetition vocab, AI-graded writing, descriptive scenes, and CPC terminology). Foundations and most training modes work offline; writing and scene grading require the API key above.