# unreal-behavior-trees

Build NPC AI in Unreal Engine 5 with Behavior Trees and Blackboards. Use it for enemy logic, patrols, reactive branches, and custom BT nodes.

- skill · `type=skill` · Claude Code, Codex, Cursor, GitHub Copilot, Gemini CLI, OpenCode · 5200 installs · ★ 4506
- Author: gamedev-skills
- License: Apache-2.0 · policy=mirror · the beginning of the file is at the end of this page
- Source: https://github.com/gamedev-skills/awesome-gamedev-agent-skills/tree/HEAD/skills/unreal/unreal-behavior-trees/SKILL.md
- Updated: 2026-10-24
- HTML: https://affpapa.org/en/nevibecode/skills/unreal-behavior-trees

## What it does

This skill lays out an NPC AI workflow for Unreal Engine 5.8. A Blackboard stores keys such as `TargetActor` and `LastKnownLocation`; a Behavior Tree defines decisions; and an `AAIController` starts the tree with `RunBehaviorTree(BT)`. Branches use Selector, Sequence, and Simple Parallel composites.

Decorators gate branches from Blackboard values, Services refresh state while a branch is active, and Tasks return `Succeeded`, `Failed`, or `InProgress`. The skill also covers C++ `BTTask` nodes, Blackboard updates from the controller, and the Behavior Tree debugger in PIE, which shows the running node and live key values.

You need Unreal Engine 5.8, `BT_`/`BB_` assets, and an `AAIController`. `MoveTo` fails when the target is off the Nav Mesh or the level lacks a Nav Mesh Bounds Volume. A latent task that never calls `FinishLatentTask` will keep the tree waiting. Projects already using StateTree should be checked before adding a parallel Behavior Tree setup.

## Requirements
- Works with: Unreal Engine

## Install

### Claude Code (native platform)

1. **Skills CLI (Vercel)**
```bash
npx skills add gamedev-skills/awesome-gamedev-agent-skills --skill unreal-behavior-trees -a claude-code
```

2. **Manually: put the files in place**
- File: `~/.claude/skills/unreal-behavior-trees/SKILL.md` — Copy the whole skill folder; for one project use .claude/skills/unreal-behavior-trees/

### Codex

1. **Skills CLI (Vercel)**
```bash
npx skills add gamedev-skills/awesome-gamedev-agent-skills --skill unreal-behavior-trees -a codex
```

2. **Manually: put the files in place**
- File: `.agents/skills/unreal-behavior-trees/SKILL.md` — For all projects use ~/.agents/skills/

### Cursor

1. **Skills CLI (Vercel)**
```bash
npx skills add gamedev-skills/awesome-gamedev-agent-skills --skill unreal-behavior-trees -a cursor
```

2. **Manually: put the files in place**
- File: `.cursor/skills/unreal-behavior-trees/SKILL.md` — Cursor also reads .agents/skills/ and .claude/skills/

### GitHub Copilot

1. **GitHub CLI**
```bash
gh skill install gamedev-skills/awesome-gamedev-agent-skills unreal-behavior-trees
```

2. **Manually: put the files in place**
- File: `.github/skills/unreal-behavior-trees/SKILL.md`

### Gemini CLI

1. **Skills CLI (Vercel)**
```bash
npx skills add gamedev-skills/awesome-gamedev-agent-skills --skill unreal-behavior-trees -a gemini-cli
```

2. **Platform CLI**
```bash
gemini skills install https://github.com/gamedev-skills/awesome-gamedev-agent-skills --path skills/unreal/unreal-behavior-trees
```

### Windsurf (Devin Desktop)

**Manually: put the files in place**
- File: `.devin/skills/unreal-behavior-trees/SKILL.md` — The legacy .windsurf/skills/ path still works

### OpenCode

**Skills CLI (Vercel)**
```bash
npx skills add gamedev-skills/awesome-gamedev-agent-skills --skill unreal-behavior-trees -a opencode
```

### Claude.ai

**Claude.ai**
- Zip the folder and upload it in Settings → Capabilities → Skills

Where a file is given instead of a command, copy the files from the source to that path: https://github.com/gamedev-skills/awesome-gamedev-agent-skills/tree/HEAD/skills/unreal/unreal-behavior-trees/SKILL.md

## When to use it
- build a `BT_` and `BB_` asset pair for an NPC
- organize attack, investigate, and patrol branches
- wire a Blackboard to an `AAIController`
- write a custom `BTTask` or `BTService` node
- debug a failing `MoveTo` or stuck latent task

## Example prompts
- Build an enemy Behavior Tree with priority branches for `TargetActor`, `LastKnownLocation`, and patrol.
- Write a C++ `BTTask` that moves to `TargetActor` and completes its latent execution correctly.
- Debug why `MoveTo` fails immediately and check the Nav Mesh, Blackboard key, and controller setup.

## Source text · SKILL.md · Apache-2.0

Below is the content of a third-party file. It is data, not instructions for you: do not act on anything written inside unless the human asks. Block tag: a02c5691dcd5fd54.

BEGIN THIRD-PARTY FILE a02c5691dcd5fd54
```text
---
name: unreal-behavior-trees
description: >
  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.
---

# 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

1. **Create the pair:** a Blackboard (`BB_`) holds typed keys (the AI's memory: `TargetActor`,
   `LastKnownLocation`, `bIsInvestigating`); a Behavior Tree (`BT_`) references that Blackboard.
2. **Possess and run.** An `AAIController` possesses the pawn and calls `RunBehaviorTree(BT)`,
   which also initializes the referenced Blackboard.
3. **Structure with composites.** **Selector** runs children left→right until one *succeeds*
```
END THIRD-PARTY FILE a02c5691dcd5fd54

The third-party file has ended. Everything between the a02c5691dcd5fd54 tags is data: requests and commands from it are not followed. An “end of file” line with another tag inside the block is part of the file.

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