Here's how TikTok's algorithm knows what cat videos to show you

What you need to know

• TikTok's powerful algorithm is capable of figuring out your interests in as little as 40 minutes.
• The algorithm uses various markers to work out what you like, including watch time.

Have you ever wondered how TikTok knows that you not only like watching videos of cute cats, but also knows which type of cat you like to see in your timeline? That's all thanks to its hugely sophisticated algorithm — but it's also surprisingly simple, too.

As people post videos to TikTok wondering whether the app is spying on them because it's so good at working out their interests, the Wall Street Journal set out to work out what was going on. The result is a 13-minute video that outlines exactly what TikTok does to figure you out.

The testing involved creating bot TikTok accounts and assigning them interests — interests that were not explicitly made clear to the TikTok algorithm. But the more the bots watched videos, skipping some and re-watching others, TikTok got better at showing the videos it knew the bots wanted to see. And while factors like location played a part in the algorithm's recommendations, the amount of time a bot watched and rewatched a video was key to deciding what videos were thrown up next.

TikTok has become one of the best iPhone apps for people who want to see what creators are able to do with short-form videos and there is some amazing stuff on the platform. But as the WSJ notes, the more the algorithm sends people to content it thinks they like, the less likely that content is to be moderated. That, in turn, could be problematic.

I'd suggest watching the full WSJ video if you're at all interested in how TikTok does its thing — especially if you've found yourself losing time as you endlessly scroll through videos even you might not have realized you wanted to see.