Facebook uses an internal database to track rivals, including young startups performing unusually well, people familiar with the system say. The database stems from Facebook’s 2013 acquisition of a Tel Aviv-based startup, Onavo, which had built an app that secures users’ privacy by routing their traffic through private servers. The app gives Facebook an unusually detailed look at what users collectively do on their phones, these people say.

The tool shaped Facebook’s decision to buy WhatsApp and informed its live-video strategy, they say. Facebook used Onavo to build its early-bird tool that tips it off to promising services and that helped Facebook home in on Houseparty.