Vortaro.jp, presented as Kajero, is an online multilingual Esperanto dictionary and learning resource designed to support a richer experience of studying and using Esperanto. The site describes its dictionary as containing around 230,000 words and translations, with search across multiple languages, including Japanese, English, Chinese, and Esperanto. Visitors can explore word lists, readings, an introductory guide to Esperanto, and practical links, while language settings allow the interface to be displayed in several languages.

Kajero also offers interactive tools and community learning features. Users can listen to word pronunciations, try a pronunciation challenge, and submit recordings. Learning notes support vocabulary, example sentences, grammar, questions, and other study topics; members can browse recent notes and frequently bookmarked words. The site also features a daily word, discussion posts, and guidance on how to use its resources. For users who want to help maintain and improve the dictionary and learning tools, Kajero provides a development-support option. Together, these features make Vortaro.jp a practical reference and study hub for Esperanto learners.