Find in Knowledge Base
< All Topics

Debugging Tools

Bygoktugulvan@gmail.com

Here are the specific debugging tools and workflows you need to architect for a UE5 project.

1. Master “Unreal Insights” (The Performance Truth)

The old “stat unit” commands are not enough for UE5. You must set up Unreal Insights. It is a standalone profiling tool included with the engine.

  • Trace Analysis: It records the entire application state to a trace file. You can see CPU threads, GPU timing, and Asset Loading all aligned on a timeline.
  • Asset Loading Debugging: UE5 relies heavily on streaming (World Partition). Insights will tell you exactly which texture or mesh caused a stutter when the player turned a corner.
  • Tech Lead Action: Set up a .bat file or script so your QA/Dev team can launch the game with -trace=cpu,gpu,memory parameters easily, then send you the .utrace file for analysis.

2. The Visual Logger (VisLog)

This is one of Unreal’s most powerful, underused tools (Window > Developer Tools > Visual Logger).

  • What it does: It captures a digital snapshot of the game state every frame and records it to a file.
  • The Killer Feature: You can open the file later, see a 3D replay of the game, and scrubbing the timeline shows you the exact AI logic (Behavior Tree state), physics collisions, and logs occurring at that specific frame.
  • Tech Lead Action: Enforce the use of UE_VLOG in your C++ code instead of standard logging for complex AI or movement logic.

3. Debugging New Tech: Nanite & Lumen

Nanite (geometry) and Lumen (lighting) are magic, until they break. You cannot debug them with breakpoints. You use View Modes.

  • Nanite Visualization: If your FPS drops, switch the view mode to Nanite > Overdraw. If the screen lights up white/red, your artists are stacking too many meshes on top of each other.
  • Lumen Overview: If lighting looks weird (leaking light or pitch black), use Lumen > Lumen Scene. This shows you what the engine “sees” for light bouncing. Often, you’ll find that a mesh has no “Distance Fields” generated, causing the lighting bug.

4. Gameplay Ability System (GAS) Debugging

If you are building an RPG or Shooter, you are likely using GAS. It is notoriously hard to debug because it relies on Tags and Attributes, not just code execution.

  • Console Command: showdebug abilitysystem.
  • What it does: It renders three columns of text on screen showing exactly what Gameplay Tags the actor has, what Abilities are active, and the value of Attributes (Health, Mana, etc.).
  • Tech Lead Action: Ensure your inputs allow cycling the “debug target” (PageUp/PageDown) so you can look at an enemy and see their ability system debug info, not just the player’s.

5. World Partition & Data Layers

UE5 replaced “Levels” with “World Partition” (one giant world that streams in).

  • Debug Cells: Use wp.Runtime.ToggleDrawRuntimeHash. This draws grids on the ground showing which parts of the world are loaded and which are unloaded.
  • Data Layer Debugging: If an object is missing, it’s usually on the wrong “Data Layer” (e.g., a Quest NPC is on the “Post-Game” layer but you are in the “Early-Game” state). Use the Data Layer Outliner to force toggle layers on/off at runtime to test logic.

6. The “Gauntlet” Automation Framework

For a Tech Lead, manual testing is too slow. Gauntlet is UE5’s automation framework.

  • What it does: It launches the game, runs a script (e.g., “Load level, spawn 100 bots, run to the end”), and reports performance data (FPS, Memory).
  • Tech Lead Action: Integrate Gauntlet into your CI/CD (Jenkins/TeamCity). If a commit drops the average FPS below 60 on the test map, the build should fail.

7. Blueprint vs. C++ Debugging

Your team will likely mix C++ and Blueprints. This causes “call stack hell.”

  • The Blueprint Debugger: You can set breakpoints on nodes (F9).
  • Call Stack Integration: When you crash in C++, the Visual Studio call stack often just says ProcessEvent.
  • The Fix: You must install the UnrealVS extension (comes with the engine install). It improves the debugging experience in Visual Studio specifically for UE projects.
  • Config Rule: In DefaultEngine.ini, ensure [Script/Engine.Engine] bSmoothFrameRate=false is set for dev builds. Debugging logic when the engine is throttling FPS to 30 or 60 can hide race conditions.

8. Console Variables (CVars) & Cheats

Unreal has the CheatManager class built-in.

  • Don’t write custom cheat code: Subclass UCheatManager. This class is automatically stripped out of “Shipping” builds. This saves you from the nightmare of accidentally leaving a “God Mode” button in the final game sold on Steam.
  • CVars: Use IConsoleManager to create custom variables that can be changed at runtime (e.g., MyGame.EnemyDamageMultiplier 2.0). This allows designers to tweak balance without recompiling.

Summary of the UE5 Tech Lead Stack

  1. Profiling: Unreal Insights (Mandatory).
  2. AI/State Debug: Visual Logger (UE_VLOG).
  3. Rendering: View Modes for Nanite/Lumen.
  4. Logic: showdebug abilitysystem (if using GAS).
  5. Safety: Put cheats in UCheatManager so they don’t ship to customers.