"That Is" is a Chrome extension developed by gchang327 that allows users to insert ruby-text annotations on webpages based on customized mappings. This tool assists in remembering specific text by providing annotations whenever the defined text appears on a page. Users can create personalized definitions for words, symbols, or phrases, enhancing their understanding and memory retention. Whether learning a new language or needing mnemonic aids, "That Is" offers a seamless way to annotate text without the interruptions of traditional dictionaries or reliance on translation services.

With "That Is," users can choose from pre-set mappings like hiragana to katakana, romaji to hiragana, or even create their own custom mappings tailored to their needs. This extension empowers users to enhance their browsing experience by providing personalized guides at the click of a button.