# assemblyCompilationNotRequired

> Event invoked on the main thread during a compilation pass for each assembly that is already up to date and therefore doesn't need to be recompiled.

## Definition

* **Type:** Event
* **Namespace:** [UnityEditor.Compilation](/engine/6000.6/script-reference/unityeditor/compilation.md)
* **Assembly:** UnityEditor.CoreModule

```csharp
public static event Action<string> assemblyCompilationNotRequired
```

### Remarks

A compilation pass can be triggered by modifying or reimporting scripts, entering Play mode, code reload, or when compilation is requested from code, such as via [CompilationPipeline.RequestScriptCompilation](/engine/6000.6/script-reference/unityeditor/compilation/compilationpipeline/requestscriptcompilation.md).

During a compilation pass, Unity evaluates each assembly in the project to determine whether it needs to be recompiled. For each assembly in that pass:

* If the assembly needs compiling, it gets compiled, and the [CompilationPipeline.assemblyCompilationFinished](/engine/6000.6/script-reference/unityeditor/compilation/compilationpipeline/assemblycompilationfinished.md) event is invoked for that assembly.
* If the assembly doesn't need compiling, `assemblyCompilationNotRequired` is invoked for that assembly's output path.

You can use `assemblyCompilationNotRequired` for tooling that hooks into the compilation pipeline and needs to track the state of every assembly during a pass, including assemblies that were skipped. For example:

* Post-processing or instrumentation tools that operate on assembly outputs need to know which assemblies are present and current even if they weren't rebuilt this pass.
* Build or asset pipelines that require the state of all assemblies after a compilation event.