The Wall Street Journal created dozens of automated accounts that watched hundreds of thousands of videos to reveal how the the TikTok algorithm knows you so well.

A Wall Street Journal investigation found that TikTok only needs one important piece of information to figure out what you want: the amount of time you linger over a piece of content. Every second you hesitate or rewatch, the app is tracking you.

Photo illustration: Laura Kammermann/The Wall Street Journal

WSJ video investigations use visual evidence to reveal the truth behind the most important stories of the day.

Inside TikTok’s Highly Secretive Algorithm
This WSJ video investigation reveals how the video-centric social network is so good at figuring out interests you never expressly tell it.

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