Facebook is drawing back the veil to show what data it collects on users.
Many may not like what they see.
A feature in settings called Off-Facebook Activity will show all the apps and websites that send information about you to Facebook, which is then used to target ads more effectively.
You will also be able to clear your history and prevent your future off-app behaviour being tapped. But one expert said the move was unlikely to have a big impact on the firm's profits.
For now, it is rolling out very slowly, with only Ireland, South Korea and Spain getting access. But the goal is to eventually offer it globally.
The initiative comes at a time when Apple and Mozilla have already taken steps to prevent Facebook and other services from tracking users from one online platform to another via their browsers.
In addition, Germany's competition regulator had told the firm it needed to substantially restrict the way it collected and combined data about its members unless it sought more explicit consent than it had done.