unreal-behavior-trees

Q: How do I install unreal-behavior-trees?

Run npx skills add https://github.com/gamedev-skills/awesome-gamedev-agent-skills --skill unreal-behavior-trees in your project. The skills CLI detects the agents you use and copies the skill into the right folder. For Claude Code you can also place the skill folder at ~/.claude/skills/unreal-behavior-trees/ (personal) or .claude/skills/unreal-behavior-trees/ (project).

by gamedev-skillsAI & Agents

Build NPC AI in Unreal Engine 5 with Behavior Trees and Blackboards: composites (Selector/Sequence), tasks, decorators, services, and running the tree from an AIController. Use when creating enemy/NPC AI, BT/BB assets, custom BTTask or BTService nodes, or when the user mentions Behavior Tree, Blackboard, AIController, BTTask, decorator, or service.

Installs: 5.5K
Last 24h: +294
Trending rank: #978
Security: Pass

Install

Works with every agent the skills CLI supports.

npx skills add https://github.com/gamedev-skills/awesome-gamedev-agent-skills --skill unreal-behavior-trees

01
Install
Run the command in your project. The CLI asks which agents to install for.
02
Describe the task
Ask your agent for something this skill covers. It loads unreal-behavior-trees automatically when relevant.
03
Review the result
The agent follows the SKILL.md steps, scripts and references bundled with the skill.

Security audits

Independent scans of the skill's instructions and bundled files.

Gen Agent Trust Hub PassSAFE ·No security issues detected. The skill provides legitimate technical instructions, architectural patterns, and C++ code snippets for developing AI Behavior Trees in Unreal Engine 5.

Socket PassNo alerts

Snyk PassLOW ·Risk: LOW · No issues

SKILL.md

The instructions your agent reads when the skill is triggered.

Unreal Behavior Trees

Author NPC decision-making in UE5 with Behavior Trees driven by a Blackboard: structure the tree with composites, gate branches with decorators, keep state current with services, and run it from an AIController. Targets UE 5.8.

When to use

Use when building enemy/NPC AI: creating a BT_/BB_ asset pair, structuring Selector/Sequence branches, adding decorators (conditions) and services (periodic updates), writing custom BTTask/BTService nodes, or wiring an AIController to run the tree.
Use when the project has Behavior Tree (BT_) and Blackboard (BB_) assets and an AAIController.

When not to use: the concept of AI (FSM vs BT vs steering, cross-engine) → game-ai. Pure navigation/pathing math is engine navmesh (BT's MoveTo uses it). Simple one-off logic may be cheaper as a small state machine than a full tree.

Behavior Tree or StateTree? UE 5.8 ships both, and Behavior Trees are not deprecated. StateTree is Epic's general-purpose hierarchical state machine: it combines BT-style selection with explicit States and Transitions. If the project already uses StateTree assets, or the AI is naturally a set of modes with clear transitions (patrol → alert → combat), check with the user before adding a Behavior Tree next to it. Keep using Behavior Trees where the project already has BT_/BB_ assets.

Core workflow

Create the pair: a Blackboard (BB_) holds typed keys (the AI's memory: TargetActor, LastKnownLocation, bIsInvestigating); a Behavior Tree (BT_) references that Blackboard.
Possess and run. An AAIController possesses the pawn and calls RunBehaviorTree(BT), which also initializes the referenced Blackboard.
Structure with composites. Selector runs children left→right until one succeeds (priority/fallback: "attack, else chase, else patrol"). Sequence runs children until one fails (do-all: "move to cover → reload → peek"). Simple Parallel runs one main task alongside a secondary.
Gate branches with Decorators that read Blackboard keys (e.g. "Has Target?" guards the combat branch). Set Observer Aborts so the tree re-evaluates when the key changes.
Keep the Blackboard current with Services attached to a branch — they tick periodically (e.g. update TargetActor via a sight check) only while that branch is active.
Do work in Tasks, which return Succeeded, Failed, or InProgress (latent tasks like MoveTo finish later).
Verify with the Behavior Tree debugger during PIE — it highlights the running node and shows live Blackboard values, so you see exactly which branch executes.

Patterns

1. AIController that runs the tree (C++)

void AEnemyAIController::OnPossess(APawn* InPawn)
{
    Super::OnPossess(InPawn);
    if (BehaviorTree)                 // UPROPERTY(EditAnywhere) TObjectPtr<UBehaviorTree>
        RunBehaviorTree(BehaviorTree); // initializes & uses the Blackboard the BT references
}

2. A priority tree (node structure)

ROOT
└── Selector (try combat, else investigate, else patrol)
    ├── Sequence            [Decorator: Blackboard 'TargetActor' Is Set, Observer Aborts: Both]
    │     ├── Task: MoveTo (TargetActor)          // latent: returns InProgress then Succeeded
    │     └── Task: Attack
    ├── Sequence            [Decorator: 'LastKnownLocation' Is Set]
    │     ├── Task: MoveTo (LastKnownLocation)
    │     └── Task: Wait (3s) + clear key
    └── Task: Patrol (BTTask_FindPatrolPoint -> MoveTo)

Observer Aborts: Both makes the combat branch interrupt patrol the instant TargetActor is set, and bail out when it's cleared — this is what makes the AI feel reactive.

3. Updating the Blackboard from code (e.g. on seeing the player)

void AEnemyAIController::SetTarget(AActor* Target)
{
    if (UBlackboardComponent* BB = GetBlackboardComponent())
        BB->SetValueAsObject(TEXT("TargetActor"), Target);   // key name must match the BB asset
}
// Clear with BB->ClearValue(TEXT("TargetActor")); to drop back to a lower-priority branch.

Pitfalls

AI never starts — the pawn isn't possessed (set the Pawn's Auto Possess AI to "Placed in World or Spawned" and assign the AIController), or RunBehaviorTree was never called.
MoveTo instantly fails — no NavMesh in the level (add a Nav Mesh Bounds Volume), or the target is off the navmesh.
Branch doesn't react to changes — the gating Decorator's Observer Aborts is set to None; set it to Self/Lower Priority/Both so the tree re-evaluates when the key changes.
A task hangs the tree — a custom task returned InProgress and never calls FinishLatentTask. Always complete latent tasks.
AI behaves strangely only when several NPCs share a tree — a custom task stores run state in member variables. Task nodes are shared by every AI using the asset unless instanced; keep per-AI state in node memory (see the reference).
Blackboard key typos — SetValueAsObject("Taget", ...) silently does nothing; match the key name and type exactly, or use a cached FBlackboardKeySelector.
Sequence vs Selector confusion — Sequence = AND (stops on first failure); Selector = OR (stops on first success). Swapping them inverts the behaviour.

References

For a custom C++ UBTTaskNode (instant and latent ExecuteTask returning EBTNodeResult, per-AI node memory, AbortTask, and a FBlackboardKeySelector), read references/custom-bttask.md.
Primary docs: "Behavior Trees in Unreal Engine" (https://dev.epicgames.com/documentation/en-us/unreal-engine/behavior-trees-in-unreal-engine).

Related skills

game-ai — engine-agnostic AI design (FSM, BT, steering, pathfinding choices).
unreal-cpp-gameplay — the AIController and pawn classes in C++.
fps-shooter / tower-defense — genres that compose enemy AI.

FAQ

What does the unreal-behavior-trees skill do?

How do I install unreal-behavior-trees?

Run npx skills add https://github.com/gamedev-skills/awesome-gamedev-agent-skills --skill unreal-behavior-trees in your project. The skills CLI detects the agents you use and copies the skill into the right folder. For Claude Code you can also place the skill folder at ~/.claude/skills/unreal-behavior-trees/ (personal) or .claude/skills/unreal-behavior-trees/ (project).

Which AI agents can use unreal-behavior-trees?

Any agent that supports the open Agent Skills format (a folder with a SKILL.md file), including Claude Code, Codex, Cursor, GitHub Copilot, Gemini CLI, Windsurf, Cline, OpenCode and more.

Is unreal-behavior-trees safe to install?

Security partners have reviewed it: Gen Agent Trust Hub passed; Socket passed; Snyk passed. As with any skill, read the SKILL.md and bundled scripts before installing.

Who maintains unreal-behavior-trees?

It is published by gamedev-skills in gamedev-skills/awesome-gamedev-agent-skills. It has 5,454 recorded installs.