Roslyn Script Validation

By default, MCP for Unity uses a fast structural validator for scripts the LLM generates. For strict validation that catches undefined namespaces, types, and methods at write time — without a full Unity compile — install the optional Roslyn DLLs.

Most users don't need this. Enable it when:

• You're letting the LLM write a lot of unsupervised C# and want stricter feedback loops
• You're seeing recurring compile errors that survive the structural validator
• You're building custom tools that depend on accurate symbol resolution

One-click installer (recommended)

1. Open Window → MCP for Unity.
2. Scroll to the Runtime Code Execution (Roslyn) section in the Scripts / Validation tab.
3. Click Install Roslyn DLLs.

The installer downloads the required NuGet packages, places the DLLs in Assets/Plugins/Roslyn/, and adds USE_ROSLYN to Scripting Define Symbols.

You can also trigger it from the menu: Window → MCP For Unity → Install Roslyn DLLs.

Manual install (if the installer isn't available)

1. Install NuGetForUnity.
2. Open Window → NuGet Package Manager.
3. Install:
   • Microsoft.CodeAnalysis v5.0
   • SQLitePCLRaw.core v3.0.2
   • SQLitePCLRaw.bundle_e_sqlite3 v3.0.2
4. Add USE_ROSLYN to Player Settings → Scripting Define Symbols.
5. Restart Unity.

Manual DLL install (no NuGetForUnity)

1. Download Microsoft.CodeAnalysis.CSharp.dll and its dependencies from NuGet.org.
2. Place DLLs in Assets/Plugins/Roslyn/.
3. Ensure .NET compatibility settings are correct for your Unity version.
4. Add USE_ROSLYN to Scripting Define Symbols.
5. Restart Unity.

Verifying it's active

After restart, the MCP for Unity status panel shows Roslyn: enabled under the Scripts section. The validate_script tool now performs full semantic analysis rather than the structural pass.

Disabling

Remove USE_ROSLYN from Scripting Define Symbols. The plugin falls back to structural validation; the DLLs can stay in Assets/Plugins/Roslyn/ or be removed.