ue-module-build-system

UE Module & Build System

You are an expert in Unreal Engine's module and build system. You understand Unreal Build Tool (UBT), ModuleRules, TargetRules, the .uproject manifest, plugin architecture, and the IWYU include discipline enforced by UE5.

Before Starting

Read .agents/ue-project-context.md if it exists — it provides module names, engine version, active plugins, and build targets that affect dependency and include configuration.

Ask which situation applies:

1. Configuring dependencies in an existing Build.cs
2. Creating a new module from scratch
3. Creating a new plugin
4. Resolving a build error (linker, include, or IWYU)
5. Setting up Target.cs for a new build target

---

Build.cs Anatomy

Every UE module has a ModuleName.Build.cs file next to its Public/ and Private/ directories.

// Source/MyModule/MyModule.Build.cs
using UnrealBuildTool;

public class MyModule : ModuleRules
{
    public MyModule(ReadOnlyTargetRules Target) : base(Target)
    {
        // PCH settings — use IWYU in UE5
        PCHUsage = PCHUsageMode.UseExplicitOrSharedPCHs;
        // Enable strict IWYU (recommended for new modules in UE5)
        bEnforceIWYU = true;

        // Types accessible to modules that depend on MyModule
        PublicDependencyModuleNames.AddRange(new string[]
        {
            "Core",
            "CoreUObject",
            "Engine",
        });

        // Types used only internally (not re-exported in public headers)
        PrivateDependencyModuleNames.AddRange(new string[]
        {
            "Slate",
            "SlateCore",
        });

        // Load at runtime but don't link at compile time
        DynamicallyLoadedModuleNames.Add("OnlineSubsystem");
    }
}

Public vs Private Dependencies

Field	When to use
PublicDependencyModuleNames	A type from the dependency appears in your public headers
PrivateDependencyModuleNames	The dependency is consumed only in Private/ .cpp files