Gas

🧠 Brains complement: IF an unreal-engine-skills-manager tool (external MCP) exists in this session, call it with {action: "load", skill: "gameplay-ability-system"} for UE domain knowledge (ASC setup, attribute/effect/ability APIs, networking) — treat it as the rubric for any review / "best practices" question. If no such tool is available, skip this line entirely and proceed with this skill alone — do NOT attempt the call.

Gameplay Ability System Skill

Compose, do not duplicate. Everything GAS needs already exists across Epic's engine toolsets, the generic Blueprint/Object tools, and Python. VibeUE adds no GAS wrapper service; this skill is the routing map plus the live-verified gotchas.

Ownership matrix — who does what

Python exposure facts (live-verified, UE 5.8)

• UAbilitySystemBlueprintLibrary is exposed as unreal.AbilitySystemLibrary (the "BlueprintLibrary" name does not exist in Python). asc = unreal.AbilitySystemLibrary.get_ability_system_component(actor).
• FGameplayTag cannot be constructed from raw Python: unreal.GameplayTag(tag_name=...) is rejected, TagName is read-only via set_editor_property, and GameplayTagLibrary.make_literal_gameplay_tag takes an FGameplayTag (circular). Use VibeUE's escape hatch: unreal.GameplayTagService.request_tag("A.B.C") returns the real registered tag VALUE (invalid tag for unknown names — check with GameplayTagLibrary.is_gameplay_tag_valid), and request_tag_container([...]) batches into a container. That unlocks every tag-typed API: asc.has_matching_gameplay_tag, send_gameplay_event_to_actor, assign_tag_set_by_caller_magnitude, tag-keyed TMap authoring, and tag queries. For pure READS the Epic inspector GetActiveTags also returns tag names as strings without needing tag values.
• asc.get_owned_gameplay_tags() is NOT exposed. Use the inspector.
• ASC BlueprintCallables that take a class work fine: asc.try_activate_ability_by_class(unreal.MyGA_Class) — this is the reliable Python path to drive abilities in PIE (it bypasses any component-level gates, which makes tests deterministic).
• Multiple activations inside ONE execute_python_code call happen in the same frame — no timers tick and no GE durations expire between them. Exploit this to hit caps/lockouts deterministically instead of sleeping wall-clock time.

PIE verification recipe (one round-trip per step)

pythonCopy code
import unreal, json
world = unreal.get_editor_subsystem(unreal.UnrealEditorSubsystem).get_game_world()
pawn = unreal.GameplayStatics.get_player_pawn(world, 0)
ref = json.dumps({"actor": {"refPath": pawn.get_path_name()}})
for tool in ["GetAttributeValues", "GetActiveTags", "GetActiveEffects", "GetGrantedAbilities"]:
    r = unreal.ToolsetRegistry.execute_tool("GASToolsets.AbilitySystemInspectorToolset", tool, ref)
    print(tool, r.get_value_as_json_string())
# drive an ability and re-inspect IN THE SAME CALL for deterministic assertions
asc = unreal.AbilitySystemLibrary.get_ability_system_component(pawn)
asc.try_activate_ability_by_class(unreal.MyGA_Fire)

Damage through the classic funnel also exercises GE pipelines when the project routes TakeDamage into effects: unreal.GameplayStatics.apply_damage(actor, 25.0, None, None, None).

C++ authoring gotchas (for the coding-agent handoff)

• Never call UGameplayEffect::FindOrAddComponent/AddComponent in a GE constructor — they NewObject with an empty name, which fatal-asserts at CDO construction and kills the editor on module load. In constructors use CreateDefaultSubobject<UTargetTagsGameplayEffectComponent>(TEXT("TargetTags")), call SetAndApplyTargetTagChanges(...), then GEComponents.Add(...) (protected — do it inside the class).
• SetByCaller cost/cooldown GEs: CommitAbility alone applies a 0-magnitude spec and logs a warning. Override ApplyCost/ApplyCooldown, build the spec with MakeOutgoingGameplayEffectSpec, SetSetByCallerMagnitude(tag, value), then ApplyGameplayEffectSpecToOwner.
• AbilityTags is deprecated in 5.5+ — call SetAssetTags(container) in the constructor.
• NonInstanced instancing is deprecated — default to InstancedPerActor.
• UAbilitySystemGlobals::Get().InitGlobalData() must run once at startup (GameInstance::Init / AssetManager) or target data and montage prediction fail silently.
• Set [/Script/GameplayAbilities.AbilitySystemGlobals] +GameplayCueNotifyPaths=/Game/GameplayCues in DefaultGame.ini, or the cue manager scans all of /Game/ (startup warning + cost).

Verification rules

After authoring: compile (unreal.BlueprintEditorLibrary.compile_blueprint), then prove behavior in PIE with the inspector — a successful tool call is not evidence. Attribute deltas, active-tag presence, and effect duration/stack readouts are the evidence to report.