What It Means & How to Fix It in UE5

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🧠 Why You’re Seeing This Error

This error means Unreal’s shader compiler is trying to compile a shader, but it can’t find the required main function (or whatever entry point function it’s expecting).

In UE5, this typically happens when:

• You forgot to define the main() function in your custom shader
• You used a different entry point name, but didn’t register it correctly
• You’re compiling a shader with the wrong shader stage (e.g., Vertex vs Pixel)
• Your shader file is missing or malformed
• A #ifdef block accidentally hides the main function

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💥 Example Error Message

error X3013: 'main': no matching entry point defined

Or, in more advanced cases:

error X3013: 'MainVS': no matching entry point defined

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🛠️ Common Shader Scenarios That Cause This

❌ Missing Main Function

// Shader file is missing this
void main() {
    // logic
}

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❌ Wrong Entry Point Name

void MyVertexShaderMain() {
    // logic
}

// But the compiler expects 'main' or 'MainVS'

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❌ Entry Point Hidden Behind #ifdef

#if USE_SHADER
void main() {
    // logic
}
#endif

// If USE_SHADER isn’t defined, main() disappears

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❌ Wrong Shader Stage Assigned in C++

// Requested vertex shader entry point, but only pixel shader exists

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✅ How to Fix X3013 in UE5 – Step-by-Step

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✔️ 1. Make Sure the Shader File Contains the Correct Entry Function

Basic HLSL:

void main(
    in float4 InPos : POSITION,
    out float4 OutColor : SV_Target
)
{
    OutColor = float4(1, 0, 0, 1);
}

Global shaders in UE5 often use named functions like MainVS, MainPS, etc., instead of plain main.

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✔️ 2. Confirm the Entry Point Name Matches the C++ Shader Registration

In your IMPLEMENT_SHADER_TYPE macro, make sure the entry point name is correct:

IMPLEMENT_SHADER_TYPE(, FMyVertexShader, TEXT("/Shaders/MyShader.usf"), TEXT("MainVS"), SF_Vertex);

If your shader has:

void MainVS(...) { }

…then "MainVS" must be passed as the entry point string.

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✔️ 3. Avoid #ifdef Blocks That Hide the Main Function

Make sure the entry point isn’t wrapped in a conditional that evaluates to false:

#ifdef ENABLE_SHADER
void main() { ... }
#endif

// If ENABLE_SHADER is undefined, main() is missing

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✔️ 4. Clean and Rebuild Shader Cache

Sometimes Unreal doesn’t recognize shader file changes. Run:

bashCopyEditDerivedDataCache/ → Delete contents (optional)
→ Then rebuild project

Or in editor:

Console Command: ShaderCompileWorker -clean

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✅ Summary: How to Fix “error X3013: ‘main’: no matching entry point” in UE5

Cause	Fix
Shader file has no main()	Define a valid entry point function in your HLSL code
Entry point name mismatch	Match the name in IMPLEMENT_SHADER_TYPE
Preprocessor macros hiding the function	Ensure main() isn’t wrapped in an inactive #if block
Wrong shader stage used	Match shader function to correct stage (SF_Vertex, SF_Pixel)