Chrome extension · v0.1, in development
Cairn is a Chrome extension for people working through real university lecture series — Stanford CS, MIT OCW, and the rest. It tracks your progress across devices, and surfaces traces left by other learners at the moment they were posted.
How it works
No dashboards to maintain. No streaks to break. The extension stays out of the way until you reach somewhere it can help.
Track your progress automatically.Cairn watches what you watch on YouTube and tracks it against your enrolled courses. There is no "mark complete" button to click. Sign in and your progress follows you to the next computer, picking up where you left off — at the second you left off.
Find traces from other learners.When you reach a hard moment in a lecture, see notes left by people who were there before you. Each trace is anchored to the second it was posted. It is not a chat — it is a marker on a trail. You can leave one of your own and keep walking.
Bring your own AI key.Optional. Connect an OpenRouter or Gemini key for cross-lecture explanations and short note summaries when you need them. Your key stays in your browser. Cairn never stores it, never proxies it, never sees it.
What's different
Most YouTube course tools are built for the solo note-taker. Cairn is built around the idea that other people walked this trail before you, and what they left behind can help.
A trace is a short, timestamped note pinned to a moment in a lecture. You see traces only at the seconds they were posted, and only when they are useful — at the kinds of moments where someone reached out a hand. There are no follower counts, no DMs, no replies threading off into the woods. People appear under anonymous nicknames they choose. There is nothing to perform and nothing to check.
The course catalog itself is community-curated. If a lecture series someone wanted is missing, they add it. If a playlist was reordered upstream, someone fixes it. The work of making the trail legible is shared among the people walking it.
Honest about what this is
Cairn is a free, donation-supported side project. The source is available on GitHub. There is no roadmap deck, no funding round, no growth team. It exists because the person who made it kept abandoning Stanford CS courses around lecture four, and wanted a quieter, more honest tool than the ones that exist. If that's you too — welcome. If not, that's fine. Cairn doesn't need to be for everyone.