This blog post was written in reference to Unreal Engine 5.8

Overview

Currently, there are a few ways to debug Mass within Unreal Engine:

• Mass Debugger: An experimental tool for visualizing active Processors, Entities, and high level management. In 5.8 it also has Breakpoints and Query Editor tabs.
• Gameplay Debugger: Runtime visualization of runtime data for Fragments and Entities.
• Console commands: Gated behind WITH_MASSENTITY_DEBUG, so they work in packaged development builds where the editor windows aren’t available. Useful ones include :
  • mass.PrintEntityFragments
  • mass.LogArchetypes
  • mass.LogFragmentSizes
  • mass.LogMemoryUsage
  • mass.LogKnownFragments
  • mass.debug.DebugEntity
  • mass.debug.SetFragmentBreakpoint
• Unreal Insights: Mass has trace support via MassEntityTrace.h, plus the MassInsights plugin for viewing it.

Mass Debugger

Currently, the engine provides a Mass Debugger window located in Tools>Debug>Mass Debugger and is able to help you find what Processors, Fragments, Entities, and Archetypes are being used.

To be able to see the currently running session’s data, located in the top right corner of the window, you have to either have Auto-Switch enabled or select the appropriate world from the drop-down.

Warning: 5.8 Caution

The Mass Debugger is fairly new and has some instability that can cause crashes, you have been warned!

The Mass Debugger does not automatically refresh while the application is running currently while the application is running. You have to Click the Refresh button located in the top left corner.

The Mass Debugger’s Entities tab can show the actual runtime values of Fragments for a single Entity. It’s open by default, docked next to the Archetypes tab. Use the Select Fragments dropdown to pick which Fragments become columns, then press Refresh Entity Data to pull the current values(or tick Auto Update Entity Data to keep them refreshing). Shared and Const Shared Fragments are read the same way.

Gameplay Debugger

The Gameplay Debugger is still the tool to reach for when you want that data drawn in the world during play, next to the Entity it belongs to. Press the ' key to open it, then the NumPad slot key to toggle the Mass category.

Be sure to use the onscreen inputs to change what information you’re trying to visualize.