Dart and Flutter DevTools has a documented, officially supported extensions framework that lets any pub package ship its own tab inside DevTools, built with Flutter web and reusing DevTools' own UI primitives. Packages like shared_preferences, provider, patrol, and drift already do this, but almost nobody outside the package-author community knows the framework exists, and I haven't seen a single talk on building one. In this talk I build a custom DevTools extension live for a real, relatable pain point (inspecting an app's feature-flag state at runtime), wire it into a running app, and show how any teammate gets it automatically the moment they add the pub dependency: no separate install, no separate distribution channel.