Claude-Code-Game-Studios/docs/engine-reference/unreal/plugins/gameplay-ability-system.md

Unreal Engine 5.7 — Gameplay Ability System (GAS)

Last verified: 2026-02-13 Status: Production-Ready Plugin: GameplayAbilities (built-in, enable in Plugins)

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Overview

Gameplay Ability System (GAS) is a modular framework for building abilities, attributes, effects, and gameplay mechanics. It's the standard for RPGs, MOBAs, shooters with abilities, and any game with complex ability systems.

Use GAS for:

• Character abilities (spells, skills, attacks)
• Attributes (health, mana, stamina, stats)
• Buffs/debuffs (temporary effects)
• Cooldowns and costs
• Damage calculation
• Multiplayer-ready ability replication

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Core Concepts

1. Ability System Component (ASC)

• The main component that owns abilities, attributes, and effects
• Added to Characters or PlayerStates

2. Gameplay Abilities

• Individual skills/actions (fireball, heal, dash, etc.)
• Activated, committed (cost/cooldown), and can be cancelled

3. Attributes & Attribute Sets

• Stats that can be modified (Health, Mana, Stamina, Strength, etc.)
• Stored in Attribute Sets

4. Gameplay Effects

• Modify attributes (damage, healing, buffs, debuffs)
• Can be instant, duration-based, or infinite

5. Gameplay Tags

• Hierarchical tags for ability logic (e.g., Ability.Attack.Melee, Status.Stunned)

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Setup

1. Enable Plugin

Edit > Plugins > Gameplay Abilities > Enabled > Restart

2. Add Ability System Component

#include "AbilitySystemComponent.h"
#include "AttributeSet.h"

UCLASS()
class AMyCharacter : public ACharacter {
    GENERATED_BODY()

public:
    AMyCharacter() {
        // Create ASC
        AbilitySystemComponent = CreateDefaultSubobject<UAbilitySystemComponent>(TEXT("AbilitySystem"));
        AbilitySystemComponent->SetIsReplicated(true);
        AbilitySystemComponent->SetReplicationMode(EGameplayEffectReplicationMode::Mixed);

        // Create Attribute Set
        AttributeSet = CreateDefaultSubobject<UMyAttributeSet>(TEXT("AttributeSet"));
    }

protected:
    UPROPERTY(VisibleAnywhere, BlueprintReadOnly, Category = "Abilities")
    TObjectPtr<UAbilitySystemComponent> AbilitySystemComponent;

    UPROPERTY()
    TObjectPtr<const UAttributeSet> AttributeSet;
};

3. Initialize ASC (Important for Multiplayer)

void AMyCharacter::PossessedBy(AController* NewController) {
    Super::PossessedBy(NewController);

    // Server: Initialize ASC
    if (AbilitySystemComponent) {
        AbilitySystemComponent->InitAbilityActorInfo(this, this);
        GiveDefaultAbilities();
    }
}

void AMyCharacter::OnRep_PlayerState() {
    Super::OnRep_PlayerState();

    // Client: Initialize ASC
    if (AbilitySystemComponent) {
        AbilitySystemComponent->InitAbilityActorInfo(this, this);
    }
}

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Attributes & Attribute Sets

Create Attribute Set

#include "AttributeSet.h"
#include "AbilitySystemComponent.h"

UCLASS()
class UMyAttributeSet : public UAttributeSet {
    GENERATED_BODY()

public:
    UMyAttributeSet();

    // Health
    UPROPERTY(BlueprintReadOnly, Category = "Attributes", ReplicatedUsing = OnRep_Health)
    FGameplayAttributeData Health;
    ATTRIBUTE_ACCESSORS(UMyAttributeSet, Health)

    UPROPERTY(BlueprintReadOnly, Category = "Attributes", ReplicatedUsing = OnRep_MaxHealth)
    FGameplayAttributeData MaxHealth;
    ATTRIBUTE_ACCESSORS(UMyAttributeSet, MaxHealth)

    // Mana
    UPROPERTY(BlueprintReadOnly, Category = "Attributes", ReplicatedUsing = OnRep_Mana)
    FGameplayAttributeData Mana;
    ATTRIBUTE_ACCESSORS(UMyAttributeSet, Mana)

    virtual void GetLifetimeReplicatedProps(TArray<FLifetimeProperty>& OutLifetimeProps) const override;

protected:
    UFUNCTION()
    virtual void OnRep_Health(const FGameplayAttributeData& OldHealth);

    UFUNCTION()
    virtual void OnRep_MaxHealth(const FGameplayAttributeData& OldMaxHealth);

    UFUNCTION()
    virtual void OnRep_Mana(const FGameplayAttributeData& OldMana);
};

Implement Attribute Set

#include "Net/UnrealNetwork.h"

UMyAttributeSet::UMyAttributeSet() {
    // Default values
    Health = 100.0f;
    MaxHealth = 100.0f;
    Mana = 50.0f;
}

void UMyAttributeSet::GetLifetimeReplicatedProps(TArray<FLifetimeProperty>& OutLifetimeProps) const {
    Super::GetLifetimeReplicatedProps(OutLifetimeProps);

    DOREPLIFETIME_CONDITION_NOTIFY(UMyAttributeSet, Health, COND_None, REPNOTIFY_Always);
    DOREPLIFETIME_CONDITION_NOTIFY(UMyAttributeSet, MaxHealth, COND_None, REPNOTIFY_Always);
    DOREPLIFETIME_CONDITION_NOTIFY(UMyAttributeSet, Mana, COND_None, REPNOTIFY_Always);
}

void UMyAttributeSet::OnRep_Health(const FGameplayAttributeData& OldHealth) {
    GAMEPLAYATTRIBUTE_REPNOTIFY(UMyAttributeSet, Health, OldHealth);
}

// Implement other OnRep functions similarly...

Clamping Attributes

Attribute Sets have no built-in clamping: the Data Table Min Value and Max Value columns have no effect. Clamp in the Attribute Set:

• PreAttributeChange() is called just before any modification to an attribute, and is the hook for rules like Health = Clamp(Health, 0, MaxHealth) — its NewValue is mutable.
• PreAttributeBaseChange() is called just before a change to an attribute's base value when an aggregator exists, and PostGameplayEffectExecute() just after a Gameplay Effect is executed to modify the base value — clamp base-value changes from instant effects there.

Stacking rules govern re-applications of the same Gameplay Effect; they do not bound one attribute pushed by different effects.

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Gameplay Abilities

Create Gameplay Ability

#include "Abilities/GameplayAbility.h"

UCLASS()
class UGA_Fireball : public UGameplayAbility {
    GENERATED_BODY()

public:
    UGA_Fireball() {
        // Ability config
        InstancingPolicy = EGameplayAbilityInstancingPolicy::InstancedPerActor;
        NetExecutionPolicy = EGameplayAbilityNetExecutionPolicy::ServerInitiated;

        // Tags
        // ⚠️ UNVERIFIED FOR 5.7 — `AbilityTags` may be deprecated in favour of
        // SetAssetTags()/GetAssetTags(); the change is believed to have landed
        // around 5.5.
        // NOT SOURCEABLE — the 5.7 tag API for abilities is not covered by
        // docs/engine-reference/unreal/ (no 5.7 API dump). Verify against the UE
        // 5.7 docs before using this snippet, and correct both occurrences (here
        // and in "Use Tags in Abilities") together.
        AbilityTags.AddTag(FGameplayTag::RequestGameplayTag(FName("Ability.Attack.Fireball")));
    }

    virtual void ActivateAbility(const FGameplayAbilitySpecHandle Handle, const FGameplayAbilityActorInfo* ActorInfo,
        const FGameplayAbilityActivationInfo ActivationInfo, const FGameplayEventData* TriggerEventData) override {

        if (!CommitAbility(Handle, ActorInfo, ActivationInfo)) {
            // Failed to commit (not enough mana, on cooldown, etc.)
            EndAbility(Handle, ActorInfo, ActivationInfo, true, true);
            return;
        }

        // Spawn fireball projectile
        SpawnFireball();

        // End ability
        EndAbility(Handle, ActorInfo, ActivationInfo, true, false);
    }

    void SpawnFireball() {
        // Spawn fireball logic
    }
};

Grant Abilities to Character

void AMyCharacter::GiveDefaultAbilities() {
    if (!HasAuthority() || !AbilitySystemComponent) return;

    // Grant abilities
    AbilitySystemComponent->GiveAbility(FGameplayAbilitySpec(UGA_Fireball::StaticClass(), 1, INDEX_NONE, this));
    AbilitySystemComponent->GiveAbility(FGameplayAbilitySpec(UGA_Heal::StaticClass(), 1, INDEX_NONE, this));
}

Activate Ability

// Activate by class
AbilitySystemComponent->TryActivateAbilityByClass(UGA_Fireball::StaticClass());

// Activate by tag
FGameplayTagContainer TagContainer;
TagContainer.AddTag(FGameplayTag::RequestGameplayTag(FName("Ability.Attack.Fireball")));
AbilitySystemComponent->TryActivateAbilitiesByTag(TagContainer);

---

Gameplay Effects

Create Gameplay Effect (Damage)

// Create Blueprint: Content Browser > Gameplay > Gameplay Effect

// OR in C++:
UCLASS()
class UGE_Damage : public UGameplayEffect {
    GENERATED_BODY()

public:
    UGE_Damage() {
        // Instant damage
        DurationPolicy = EGameplayEffectDurationType::Instant;

        // Modifier: Reduce Health
        FGameplayModifierInfo ModifierInfo;
        ModifierInfo.Attribute = UMyAttributeSet::GetHealthAttribute();
        ModifierInfo.ModifierOp = EGameplayModOp::Additive;
        ModifierInfo.ModifierMagnitude = FScalableFloat(-25.0f); // -25 health

        Modifiers.Add(ModifierInfo);
    }
};

Apply Gameplay Effect

// Apply damage to target
if (UAbilitySystemComponent* TargetASC = UAbilitySystemBlueprintLibrary::GetAbilitySystemComponent(Target)) {
    FGameplayEffectContextHandle EffectContext = AbilitySystemComponent->MakeEffectContext();
    EffectContext.AddSourceObject(this);

    FGameplayEffectSpecHandle SpecHandle = AbilitySystemComponent->MakeOutgoingSpec(
        UGE_Damage::StaticClass(), 1, EffectContext);

    if (SpecHandle.IsValid()) {
        AbilitySystemComponent->ApplyGameplayEffectSpecToTarget(*SpecHandle.Data.Get(), TargetASC);
    }
}

---

Gameplay Tags

Define Tags

Project Settings > Project > Gameplay Tags > Gameplay Tag List

Example hierarchy:

Ability
  ├─ Ability.Attack
  │   ├─ Ability.Attack.Melee
  │   └─ Ability.Attack.Ranged
  ├─ Ability.Defend
  └─ Ability.Utility

Status
  ├─ Status.Stunned
  ├─ Status.Invulnerable
  └─ Status.Silenced

Use Tags in Abilities

UCLASS()
class UGA_MeleeAttack : public UGameplayAbility {
    GENERATED_BODY()

public:
    UGA_MeleeAttack() {
        // This ability has these tags
        AbilityTags.AddTag(FGameplayTag::RequestGameplayTag(FName("Ability.Attack.Melee")));

        // Block these tags while active
        BlockAbilitiesWithTag.AddTag(FGameplayTag::RequestGameplayTag(FName("Ability.Attack")));

        // Cancel these abilities when activated
        CancelAbilitiesWithTag.AddTag(FGameplayTag::RequestGameplayTag(FName("Ability.Defend")));

        // Can't activate if target has these tags
        ActivationBlockedTags.AddTag(FGameplayTag::RequestGameplayTag(FName("Status.Stunned")));
    }
};

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Cooldowns & Costs

Add Cooldown

// In Ability Blueprint or C++:
// Create Gameplay Effect with Duration = Cooldown time
// Assign to Ability > Cooldown Gameplay Effect Class

Add Cost (Mana)

// Create Gameplay Effect that reduces Mana
// Assign to Ability > Cost Gameplay Effect Class

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Common Patterns

Get Current Attribute Value

float CurrentHealth = AbilitySystemComponent->GetNumericAttribute(UMyAttributeSet::GetHealthAttribute());

Listen for Attribute Changes

AbilitySystemComponent->GetGameplayAttributeValueChangeDelegate(UMyAttributeSet::GetHealthAttribute())
    .AddUObject(this, &AMyCharacter::OnHealthChanged);

void AMyCharacter::OnHealthChanged(const FOnAttributeChangeData& Data) {
    UE_LOG(LogTemp, Warning, TEXT("Health: %f"), Data.NewValue);
}

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Sources

• https://docs.unrealengine.com/5.7/en-US/gameplay-ability-system-for-unreal-engine/
• Clamping: Gameplay Attributes and Attribute Sets https://dev.epicgames.com/documentation/en-us/unreal-engine/gameplay-attributes-and-attribute-sets-for-the-gameplay-ability-system-in-unreal-engine ; UAttributeSet API https://dev.epicgames.com/documentation/en-us/unreal-engine/API/Plugins/GameplayAbilities/UAttributeSet ; PreAttributeChange https://dev.epicgames.com/documentation/en-us/unreal-engine/API/Plugins/GameplayAbilities/UAttributeSet/PreAttributeChange
• https://github.com/tranek/GASDocumentation (community guide)