Tenkai is an online Japanese-learning platform designed to help learners look up vocabulary, understand grammar, and retain what they study. Its bilingual dictionary covers more than 300,000 words, with readings, meanings, example sentences, and pitch-accent information for over 99,000 entries. Learners can also consult a grammar reference featuring 785 points, including explanations of how forms are built, their register, and common mistakes.

To support ongoing study, Tenkai offers spaced-repetition reviews that schedule vocabulary practice and quizzes that test recall. The site includes tools and resources for browsing kanji, kana, conjugations, grammar, and other reference topics. Learners can explore Japanese text, scan a photo of Japanese writing for free without an account, and import decks when switching from jpdb. Tenkai also helps students follow textbooks such as Genki, Minna no Nihongo, and Tobira by showing the grammar points covered in each chapter. New users can create a free account for access to the Wakaba course for beginners, while additional features include reading and discovery tools, mock exams, and study dashboards.