ImprovedTube is a feature-rich browser extension (Chrome, Firefox, Edge, Opera, Whale, Safari) that extensively modifies YouTube's web interface. It implements 90+ user-facing features spanning player controls (forced playback speed, codec/AV1 blocking, PiP, cinema/theater modes, screenshots, repeat/rotate buttons), UI decluttering (hiding ads, Shorts, comments, thumbnails, sidebars, channel sections), visual theming (dark/night/black themes via CSS-variable overrides), ~35 customizable keyboard shortcuts, playback analytics, blocklists, and a sophisticated 'Smart Speed' engine that auto-skips or accelerates segments by querying the public SponsorBlock API (with k-anonymity SHA-256 hashing) and deriving speech/non-speech segments from caption and heatmap data. The extension targets www.youtube.com exclusively and has no server-side component; all state lives in chrome.storage.local with optional Google API key integration for video metadata and a Gemini-powered 'ask' feature. Architecture is a Manifest V3 WebExtension split into two execution worlds: js&css/extension/* runs in the isolated extension context (background.js service worker, chrome.storage management, feature wiring, settings migration), while js&css/web-accessible/* is injected into YouTube's main page world where it directly manipulates the DOM and the YouTube player API. Cross-world communication is handled by a hidden-DOM CustomEvent message bridge. The options/popup UI (menu/) is built on Satus, a custom declarative UI framework bundled in the repo, which is the single most reusable artifact. Settings are applied by setting html[it-*] attributes on the document root, consumed by a pervasive attribute-gated CSS system. External dependencies include YouTube's internal InnerTube API for playlist edits, the YouTube Data API v3 (with a hardcoded default API key), SponsorBlock API, Return YouTube Dislike API, Google Gemini, and browser storage APIs. The codebase is actively maintained — recent commits and issue-referenced CSS workarounds show a constant arms race against YouTube DOM changes — but carries significant technical debt: a monolithic player.js, duplicated legacy (extension.features) and modern (ImprovedTube.*) codebases, brittle tests that string-slice production source files, hardcoded credentials, dead commented code, and inconsistent i18n coverage across locales.