GAS Attributes and Effects

Select the representation

Read references/attribute-model.md and references/effect-selector.md.

• Use an Attribute for replicated numeric gameplay state that participates in GAS calculations and temporary modifiers.
• Use an Instant Gameplay Effect for a permanent base-value change such as damage, healing, or initial values.
• Use a Duration Gameplay Effect for a timed modifier or periodic effect.
• Use an Infinite Gameplay Effect for a removable modifier with no automatic expiry.
• Use SetByCaller when runtime code supplies one named magnitude to an effect spec.
• Use a Modifier Magnitude Calculation for one reusable magnitude computation.
• Use a Gameplay Effect Execution Calculation for authoritative multi-attribute or multi-output calculations such as damage resolution.

Execute

1. Define AttributeSets in native code and group attributes by coherent lifetime/ownership.
2. Initialize through an applied Gameplay Effect, not ad hoc direct writes spread across constructors and possession code.
3. Build a Gameplay Effect asset as immutable configuration; create a Gameplay Effect Spec for runtime level, context, captured values, and SetByCaller magnitudes.
4. Apply effects through an Ability System Component using correct source and target context.
5. Clamp invariants explicitly. The AttributeSet system has no automatic min/max clamp.
6. Replicate player-visible attributes and notify GAS correctly so prediction corrections and listeners remain valid.
7. Drive UI from ASC attribute-change delegates; do not poll every frame.
8. Test removal, expiry, stacking, respawn/reinitialization, prediction correction, and server/client values.

Read references/calculations-and-patterns.md for damage, healing, regeneration, buff, debuff, and initialization patterns. Read references/replication-ui.md for replication and UI.

Hard rules

• Gameplay Effect assets are definitions; do not mutate their shared defaults at runtime.
• Do not write temporary buffs directly into Attribute values.
• Do not rely on Data Table MinValue/MaxValue columns for clamping.
• Treat Instant effects as base-value changes; timed/infinite modifiers affect current values while active.
• Re-check critical invariants where final executed values are known; PreAttributeChange alone is not a universal final clamp.
• Keep gameplay authority on the server even when UI predicts or displays local changes.
• Do not poll attributes on Tick for UI.

Use references/troubleshooting.md when values double, fail to revert, exceed bounds, fail to replicate, or disagree across machines. See references/sources.md for the UE 5.8 source trail.