Most browser extensions that call an external API route your data through their own server. That's how they log usage, build analytics, gate features behind subscriptions, and eventually get acquired or shut down. I didn't want that architecture for rabbitholes.
rabbitholes is a Chrome extension that renders inline explanations for any text you highlight. The privacy design is simple: your browser talks directly to api.anthropic.com and api.search.brave.com. No intermediary server exists. There's nothing to breach, no company database holding your query history, no subscription to cancel when the startup pivots.
The technical consequence of that choice is that you supply your own Anthropic API key. It's stored in chrome.storage.sync, which Chrome encrypts and ties to your Google account — it never leaves the browser. The extension is Manifest V3, so the service worker model means there's no persistent background process phoning home.
What the extension actually does: highlight any text on any page, and a shadow-DOM tooltip appears next to your cursor with an explanation from Claude Haiku 4.5. Shadow DOM so nothing bleeds into the host page's styles or layout. Click any word in the explanation to go deeper. Drag across a phrase to explore that instead. Every answer surfaces two suggested rabbit-hole topics — the most interesting threads from that explanation — one click away. A counter tracks how many hops deep you've gone.
The Globe icon re-runs the query enriched with Brave Search results, with source chips you can click through. The Pencil icon opens a follow-up input that inherits your current context. Neither of those interactions routes through anything I control.
Zero analytics. Zero telemetry. I have no idea how many people use this or what they look up, which is the point.