How BitTorrent finds torrents

When you click a magnet link on a website to get a torrent, it automagically opens a torrent file with a list of files you can download. Ever wonder how uTorrent finds that file in the big mess of the peer to peer internet? You can now see how this works  with a new visualization in the Project Maelstrom Browser, using real-time data from µTorrent’s core.

Note: For a more technical description of how DHT lookups work, I suggest you watch this video.

What’s going on here?


Well, lots! µTorrent does all kinds of complicated stuff behind the scenes, but let’s talk about what you can see it doing in this visualization. Here’s the setup: You click on a magnet link, and Project Maelstrom searches the network of other users who have that torrent. The “target” in the center of the screen is the torrent that you’re looking for. All of the dots that are shown are the people µTorrent has asked to try and track down your “target”.

How does µTorrent actually find a torrent?

Looking up a torrent is quite a complex task, but the basic idea is kind of like this:  you walk into the biggest party in the world, looking for someone you’ve never met before. – I know that sounds a little strange, but stay with me – You’re at a party looking for a person, and you ask someone, “Hey, I’m looking for Sarah. Do you know her? Or do you know anyone that knows her?”. They reply, “Sorry, I don’t know her, but go ask Joe, Mary, and Dan over there, I think they might know her”. You then ask Joe, Mary, and Dan the same question and keep following this process until you finally find Sarah. Except, unlike you, a torrent client can ask more than 50 people every millisecond.

In this explanation, there are a few things that don’t quite fit, exactly. First, the person you’re looking for is actually the torrent. Second, there aren’t really any names in the µTorrent world — everyone you ask for help is actually anonymous. Third, and definitely not last, you actually (hopefully) find a bunch of “Sarahs” (people who have the torrent you’re looking for). But, hey, it’s a pretty close analogy.

What do all those dots mean anyway?

All those dots are other users. This is what peer-to-peer is all about—people!  Let’s take a look at this visualization right before the torrent is found, to explain exactly what is being shown in the graphic.


 Asked 29 People: Project Maelstrom has asked 29 total people, “Hey, do you know who I can download this torrent from?”

19 People Helped: 19 people that you asked replied, “Sorry, I don’t know where you can download that from, but I think I know someone who can help you find it, go ask them!”

17 People Know Where it is: 17 people that you asked replied, “I know where that torrent is, here’s a list of people that you can try downloading it from.”

Once you’ve found people to download your torrent from, you ask them to transfer the file to you. As soon as you receive enough data, the torrent loads.  A people-powered web, there it is!

See it for yourself

If you want to see this visualization in action, download Project Maelstrom and try it out for yourself! Happy Torrenting!

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Corey Dawson Hall
Written by: Corey Dawson Hall

Corey is a UX Designer of Project Maelstrom at BitTorrent, Inc.

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7 Responses to “How BitTorrent finds torrents”

  1. sdf

    Nice. Why BT don`t make a password manager using BT tech to sync your pass with all devices? Like sync your pass from pc to notebook and mobile for windows, linux, android…….
    I try Bleep and works ok, but that app need more features like groups, stickers and other things. Just copy other messengers, its the norm this days. Good luck guys.

    • Christian

      Thanks sdf, we’re always working on new ideas and way to improve current products. Your feedback is very valuable. Keep an eye our blog for future developments.

  2. Michael Pollard

    Where the cache is kept and how it’s used – and more to the point, how to get to the files if I have a problem playing them inside the browser – isn’t clear. After the “Finding Torrent” page, it gives a link to the download, but saving that starts downloading the (often huge) file over again rather than linking to the completed or partially-completed) download. The media page often finds and downloads the media, but the download link sits either “Starting…” or “0.0/x.x GB”. And sometimes, the “Finding Torrent” accumulates a lot of information and stays there. I’ve seen over a hundred “people” with over 50 “know[ing] where it is”, but it never progresses.

    But considering that it’s now December and the last version date on the Download page is May, maybe the project is stalled?

  3. BooBoo65

    It’s either have maelstrom working 100% or have magnet links work with their torrent client. I think a lot of people are going to keep magnet links working with their torrent client and not get the full experience of maelstrom.


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