Logging¶

When the visual debuggers aren't enough, the GAS log output tells you exactly what the system is doing internally.

Log Categories¶

GAS defines three log categories in AbilitySystemLog.h:

Plus the cue-specific category from GameplayCueNotifyTypes.h:

Enabling Verbose Logging¶

At Runtime (Console)¶

Log LogAbilitySystem Verbose
Log LogGameplayEffects Verbose
Log LogGameplayCueNotify Verbose

To go even deeper:

Log LogAbilitySystem VeryVerbose

The three verbosity levels for GAS:

Via Command Line¶

-LogCmds="LogAbilitySystem Verbose, LogGameplayEffects Verbose"

In DefaultEngine.ini¶

[Core.Log]
LogAbilitySystem=Verbose
LogGameplayEffects=Verbose

Key Log Messages to Watch For¶

These are the messages that most often point to the root cause of common issues:

Ability Activation¶

LogAbilitySystem: Warning: Can't activate ability [GA_MyAbility] because it's blocked by tags
LogAbilitySystem: Warning: Can't activate ability [GA_MyAbility] - failed cost check
LogAbilitySystem: Warning: Can't activate ability [GA_MyAbility] - on cooldown
LogAbilitySystem: Warning: InternalTryActivateAbility failed: [GA_MyAbility] returned false from CanActivateAbility

Effect Application¶

LogAbilitySystem: Verbose: Applied [GE_Damage] to [TargetActor], handle [42]
LogAbilitySystem: Warning: SetByCaller Magnitude for tag [SetByCaller.Damage] was not set. Using 0.
LogAbilitySystem: Warning: Attempted to apply GE with execution but no execution class set

Cue Handling¶

LogAbilitySystem: Warning: Missing gameplay cue handler for tag [GameplayCue.Hit.Physical]
LogGameplayCueNotify: Warning: GameplayCueNotify [GC_Hit_Physical] not found in any GameplayCueSet

Prediction¶

LogAbilitySystem: Verbose: Prediction key [42] confirmed by server
LogAbilitySystem: Warning: Prediction key [42] rejected - rolling back effects

The ABILITY_LOG Macro¶

GAS uses a custom macro for internal logging:

ABILITY_LOG(Verbosity, Format, ...)

This maps to UE_LOG(LogAbilitySystem, ...). If you're adding logging to your own ability code, you can use either this macro or standard UE_LOG.

Visual Logger¶

The Visual Logger (VLogAbilitySystem category) provides a timeline-based view of ability system events, particularly useful for attribute changes.

Enabling¶

1. Window > Developer Tools > Visual Logger (or vislog console command)
2. Start recording (the red button)
3. Play through your scenario
4. Stop recording and browse the timeline

Attribute Graphs¶

The ABILITY_VLOG_ATTRIBUTE_GRAPH macro (in AbilitySystemLog.h) logs attribute changes as plotted data points in the Visual Logger. When enabled, you get a graph showing attribute values over time -- very useful for debugging gradual changes, regen, DoTs, and modifier stacking.

What to Look For¶

• Sudden drops: Instant damage or cost application
• Gradual decline: Periodic effects (DoTs, stamina drain)
• Plateaus: Attribute not changing when it should (missing modifier?)
• Spikes: Unexpected values (modifier misconfiguration, stack overflow)

Filtering Log Output¶

The ability system can be noisy at verbose levels. Filter effectively:

By Category¶

Only show GAS-related logs:

Log LogAbilitySystem Verbose
Log LogGameplayEffects Verbose
Log LogNet Off           // Silence networking noise
Log LogPlayerController Off  // Silence input noise

By Actor¶

In C++, many log lines include the actor name. Use the output log filter in the editor to search for your specific actor.

By Keyword¶

Search the output log for:

• "CanActivate" -- activation failures
• "SetByCaller" -- magnitude issues
• "PredictionKey" -- prediction flow
• "GameplayCue" -- cue routing
• "ApplyGameplayEffect" -- effect application

Related Pages¶

• ShowDebug AbilitySystem -- visual debugging
• Gameplay Debugger -- per-actor inspection
• Troubleshooting -- symptom-based solutions