Unreal Engine

Unreal Engine Development Assistant

When to Use

Use this skill when:

• Developing C++ code for Unreal Engine 5.x projects
• Writing Actors, Components, or UObject-derived classes
• Optimizing performance-critical code in Unreal Engine
• Debugging memory leaks or garbage collection issues
• Implementing Blueprint-exposed functionality
• Following Epic Games' coding standards and conventions
• Working with Unreal's reflection system (UCLASS, USTRUCT, UFUNCTION)
• Managing asset loading and soft references

Do not use this skill when:

• Working with Blueprint-only projects (no C++ code)
• Developing for Unreal Engine versions prior to 5.x
• Working on non-Unreal game engines
• The task is unrelated to Unreal Engine development

Core Philosophy: Zero Assumptions

CRITICAL: Never make assumptions about the user's project. Every Unreal project is unique in structure, assets, and configuration. Always verify before suggesting code or assets.

UCLASS / USTRUCT File Creation Policy

NEVER autonomously create new UCLASS or USTRUCT header/source files.

Unreal Engine generates these files with engine-managed boilerplate that cannot be reliably replicated by hand:

• GENERATED_BODY() macro and UHT-managed include order
• Module API export macros (PROJECTNAME_API)
• Correct .generated.h include placement
• Blueprint asset registration hooks

Correct workflow:

1. User creates the class from Unreal Editor (Tools → New C++ Class or Content Browser)
2. Engine generates the .h / .cpp pair with proper boilerplate
3. Claude works on the generated files — adding members, functions, logic

If a new class is needed, tell the user to create it from the editor and describe exactly which parent class to choose. Do not generate the file yourself.

Helper Function Usage Policy

Before calling any helper function, verify it is declared in the existing codebase.

Do not assume helper functions exist (e.g. GetUIManager(), GetInventory()). Always check first using Pre-Flight Step 4. If the function is not found, use the direct Unreal API instead of inventing the call.

// ✅ Confirmed declared in codebase — use it
UIManager = GetUIManager();

// ✅ Not found in codebase — use direct API instead
UIManager = GetLocalPlayer()->GetSubsystem<UMyLocalUISubsystem>();

// ❌ Assumed to exist without verification — causes linker error if missing
UIManager = GetUIManager();

Engine API Usage Policy

Do not guess Getter functions or utility methods on engine classes without verifying they exist.

Engine APIs often lack Getters where you'd expect them by naming convention alone. When uncertain, access member variables directly or verify the API via web search before writing code. GAS-related classes (FGameplayAbilityActorInfo, FGameplayEffectSpec, etc.) are particularly prone to this — their access patterns frequently differ from standard UE conventions.

Build Verification Policy

After modifying any C++ file, run the project build and verify it succeeds before proceeding.

Check CLAUDE.md for the project-specific build command.

Pre-Flight Discovery Protocol

When a user asks for Unreal Engine help, ALWAYS execute this discovery sequence FIRST:

1. Locate the .uproject File

find . -maxdepth 2 -name "*.uproject" -type f

If found, extract:

• Engine version from "EngineAssociation" field
• Enabled plugins from "Plugins" array
• Module dependencies from "Modules" array

2. Map the Project Structure

Standard Unreal project layout:

ProjectRoot/
├── ProjectName.uproject
├── Source/
│   └── ProjectName/
│       ├── Public/            ← Header files (.h)
│       ├── Private/           ← Implementation files (.cpp)
│       └── ProjectName.Build.cs
├── Content/
│   ├── Blueprints/
│   ├── Input/                 ← Input Actions & Mapping Contexts
│   ├── Characters/
│   └── UI/
├── Config/
│   ├── DefaultEngine.ini
│   ├── DefaultInput.ini
│   └── DefaultGame.ini
└── Plugins/

3. Discover Sources and Content Assets

# C++ source files
view Source/*/Public
view Source/*/Private
find Source -name "*.h" -o -name "*.cpp" | head -20

# Engine version & plugin check
grep "EngineAssociation" *.uproject
grep -i "GameplayAbilities" *.uproject

# Content assets
find Content -type f -name "*.uasset" | head -50
find Content -type f -name "*IA_*" -o -name "*InputAction*"
find Content -type f -name "*IMC_*" -o -name "*InputMappingContext*"
find Content -type f -name "BP_*.uasset" | head -20

# Config
ls -la Config/

4. Understand Existing Code

Before suggesting ANY code:

• Read existing character/controller classes to understand patterns
• Check what components are already added
• Identify naming conventions (e.g., IA_ prefix for Input Actions)
• Look for existing helper classes or base classes

find Source -name "*Character.h" -o -name "*Character.cpp"

C++ Code Quality

Always verify these principles before finalizing any generated code. → Full reference: references/unreal_cpp_best_practice.md

• GC Safety: All UObject* and TObjectPtr<> members must be wrapped in UPROPERTY(). Prefer TObjectPtr<> for members, raw pointers for function parameters/return values. For non-UObject owners or cross-thread access (FRunnable, async tasks), use TStrongObjectPtr<> or FGCObject; avoid AddToRoot() as it bypasses GC.
• Reflection: Use BlueprintReadOnly by default. Only use BlueprintReadWrite when BP truly needs write access.
• Tick: Disabled (bCanEverTick = false) by default. Prefer timers or events.
• Casting: Never Cast<T>() in hot loops. Cache in BeginPlay or PostInitializeComponents.
• Soft References: Use TSoftClassPtr / TSoftObjectPtr instead of hard TSubclassOf for large assets.

Naming Conventions

Follow Epic Games' coding standard. Identify the project's existing convention first (Step 4).

Input System (Enhanced Input)

→ Full reference: references/enhanced_input.md

NEVER assume input action names. Always run discovery (Step 3) first.

Key points:

• Bind in SetupPlayerInputComponent using UEnhancedInputComponent
• Add UInputMappingContext via UEnhancedInputLocalPlayerSubsystem in BeginPlay
• Declare UInputAction* properties as BlueprintReadOnly
• .uasset files are binary — use find to discover, not to read

Gameplay Ability System (GAS)

→ Full reference: references/gameplay_ability_system.md

Check .uproject for "GameplayAbilities" plugin before proceeding.

Key points:

• Add GameplayAbilities, GameplayTags, GameplayTasks to Build.cs
• Place ASC on Character (single-player) or PlayerState (dedicated server)
• Grant abilities on server only (HasAuthority())
• Use FGameplayTag for ability identification over string names
• Custom AbilityTask creation: see reference → "Custom AbilityTask" section
• GA lifecycle (End vs Cancel semantics, dynamic grant/revoke): see reference → "Advanced GA Lifecycle"
• Server-authoritative activation (no client prediction): see reference → "Network Patterns"

Plugin Guidance

→ Full reference: references/plugin_guidance.md

• Always verify plugin is enabled in .uproject before writing plugin-dependent code
• For unknown or experimental plugins, search documentation and be transparent about uncertainty
• Check plugin stability status (Stable / Beta / Experimental) before use in production

Plugin Development

→ Full reference: references/plugin_development.md

For creating new UE plugins (not just using existing ones). Key points:

• Runtime/Editor module split (.uplugin Modules array)
• WITH_EDITOR macro for editor-only code isolation
• Build.cs inter-module dependency configuration (Public vs Private)
• How to add plugin module dependencies from external projects

Data-Driven Design

→ Full reference: references/data_driven_design.md

For DataAsset / DataTable based gameplay data architecture. Key points:

• UDataAsset vs UPrimaryDataAsset selection criteria
• Defining gameplay parameters with DataAssets (weapons, skills, items, etc.)
• DataTable + CSV/JSON import workflow
• DataAsset runtime loading via AssetManager

Debugging

→ Full reference: references/debugging.md

• Use UE_LOG with custom log categories (DEFINE_LOG_CATEGORY) for contextual filtering
• Use GEngine->AddOnScreenDebugMessage() for quick in-editor feedback
• Use Visual Logger for AI and spatial debugging (UE_VLOG_* macros)
• Prefer check() / ensure() over silent failures

API Knowledge Gaps

When uncertain about API usage:

1. Search Epic's documentation: web_search: "Unreal Engine [ClassName] API [EngineVersion]"
2. Search community resources: web_search: "Unreal Engine [feature] example code C++"
3. Check Epic Developer Community forums
4. Reference example projects: Lyra, Valley of the Ancient, ActionRPG

Version-Specific Considerations

Always check .uproject for "EngineAssociation":

When suggesting code, verify feature availability:

web_search: "Unreal Engine [feature] [version] availability"

Common Pitfalls

→ Full reference: references/common_pitfalls.md

• Never assume asset names or paths — always discover with find
• Missing UPROPERTY() → silent GC collection
• Cast<T>() in Tick → severe performance cost
• Hard TSubclassOf references → forced asset loading at startup
• BlueprintReadWrite on internal state → fragile BP/C++ boundary

Workflow Decision Tree

User asks for Unreal help
    │
    ├─> Find .uproject ─> Extract version & plugins
    │
    ├─> Map project structure ─> View Source/ and Content/
    │
    ├─> Identify question type:
    │   ├─> Input system?       ─> references/enhanced_input.md
    │   ├─> GAS-related?        ─> references/gameplay_ability_system.md
    │   ├─> Plugin development? ─> references/plugin_development.md
    │   ├─> Plugin usage?       ─> references/plugin_guidance.md
    │   ├─> DataAsset/DataTable? ─> references/data_driven_design.md
    │   ├─> Debugging?          ─> references/debugging.md
    │   ├─> C++ quality?        ─> references/unreal_cpp_best_practice.md
    │   └─> General C++?        ─> Read existing classes for patterns
    │
    ├─> Provide solution with:
    │   ├─> Verified asset references
    │   ├─> Version-appropriate code
    │   └─> Project-specific patterns
    │
    └─> If uncertain about API/plugin ─> Search documentation

Checklists

Pre-Code Checklist

Before providing ANY code suggestion:

• Found and read .uproject file
• Identified engine version
• Mapped Source/ directory structure
• Discovered Content/ assets (especially for input/blueprints)
• Read existing class files for patterns
• Verified asset paths and names
• Checked plugin availability
• Searched documentation for uncertain APIs
• Used project-specific naming conventions

Pre-PR / Code Review Checklist

Before finalizing any C++ code:

• Does this Actor need to Tick? Can it be replaced with a Timer or event?
• Are all UObject* and TObjectPtr<> members wrapped in UPROPERTY?
• Are hard references (TSubclassOf) causing load chains? Can they be TSoftClassPtr?
• Are Cast<T>() calls cached in BeginPlay, not repeated in Tick?
• Are Blueprint-exposed properties using the appropriate access specifier (ReadOnly vs ReadWrite)?
• Did you clean up delegates in EndPlay?
• Did you run the build and verify it succeeds? (check CLAUDE.md)

Reference Files

Load the appropriate reference file when deeper detail is needed: