Reading about the Treaty of Westphalia and hit 'Augsburg Settlement'? You half-know it. Not enough to keep going, too minor to open a new tab for. So you skim past it and the paragraph lands 20% as hard as it should.
rabbitholes is a Chrome extension that fixes that gap. Highlight any text and a shadow-DOM tooltip renders an explanation next to your cursor — no new tab, no broken focus, no host-page pollution. The explanation comes from Claude Haiku 4.5 directly from your browser to api.anthropic.com; there's no intermediary server.
The part I use most: click any word inside the explanation to go one level deeper. Drag across a phrase to pick a chunk. Each answer ends with two suggested threads — the most interesting places to go from here. The extension tracks how many hops deep you've gone, and if you keep clicking you'll eventually hit philosophy.
When you want more than a model summary, the globe icon re-answers the query enriched with Brave Search results, with source chips you can open. The pencil icon opens a follow-up input that inherits the current context as background, so you can ask a follow-on without re-explaining.
Zero analytics, zero telemetry. Your Anthropic key lives in chrome.storage.sync and never leaves the browser. Manifest V3.