Intro.js is a mature, client-side JavaScript library for creating step-by-step product tours and persistent hints on web pages. It operates entirely in the browser with no server dependencies, using a custom reactive DOM library (similar to VanJS) for state-driven UI rendering. The library exposes two main products: `introJs.tour()` for guided walkthroughs and `introJs.hint()` for annotation tooltips. Tours support dynamic step fetching, keyboard navigation, scroll-to behavior, callback hooks, and a 'don't show again' cookie feature. Hints auto-refresh on scroll/resize and can be triggered via data attributes or programmatic options. The codebase is modular, with separate packages for tour, hint, tooltip, and DOM utilities, and includes comprehensive unit tests (Jest) and visual regression tests (Cypress). While the core architecture is clean and well-tested, the library carries some legacy API surface (deprecated `introJs()` function) and outdated example integrations (Bootstrap v3, jQuery), indicating moderate technical drift. It is actively maintained with recent commits and GitHub Actions CI/CD.