The Visual Logger is a powerful debugging tool that creates and records visual representations of the gameplay state, and provides the ability to review this data in the Editor. Developers can see debug output live during a play session, or review it in the Editor after the session is over, making it much easier to resolve gameplay bugs that are hard to track down based only on user reports or game footage. The ability to record information for later review is especially important when working with rare or difficult-to-reproduce bugs. For example, an unexpected AI behavior may be caused by a game state variable that changes for a single frame can be studied after the fact by recording the data and scrubbing through the frames around the moment when the bug happened.
To activate the Visual Logger, use the menu in Windows > Developer Tools > Visual Logger. In Unreal Engine versions prior to 4.7, enter the console command "VisLog". If you are in the Editor, the Visual Logger viewport will also open.
Using the Visual Logger during a session of the Epic Games sample, StrategyGame. The purple line indicates the AI's path, and the red location marker shows the selected point in the timeline.