Example Custom MCP Tool for Unity

ConvertBuiltinMaterialsTool.cs

using Unity.AI.MCP.Editor.Helpers;
using Unity.AI.MCP.Editor.ToolRegistry;
using UnityEditor;
using UnityEngine;
using UnityEngine.Rendering;

public enum MaterialConversionScope { All, Selected }

public class ConvertBuiltinMaterialsParams {
    [McpDescription(
        "Which materials to convert: 'All' runs the project-wide upgrade; 'Selected' converts only selected Material assets.",
        Required = true,
        EnumType = typeof(MaterialConversionScope))]
    public string Scope { get; set; } = nameof(MaterialConversionScope.All);
}

public static class ConvertBuiltinMaterialsTool {
    public const string ToolName = "Unity.ConvertBuiltinMaterials";

    public const string Description =
        "Converts Built-in Render Pipeline materials to the active Scriptable Render Pipeline (URP or HDRP). " +
        "Use Scope='All' for a project-wide upgrade, or Scope='Selected' when Material assets are selected in the Project window.";

    const string MenuPathAll = "Edit/Rendering/Materials/Convert All Built-In Materials to Current SRP";
    const string MenuPathSelected = "Edit/Rendering/Materials/Convert Selected Built-In Materials to Current SRP";

    [McpTool(ToolName, Description, Groups = new[] { "assets", "rendering" }, EnabledByDefault = true)]
    public static object Handle(ConvertBuiltinMaterialsParams parameters) {
        if (parameters == null)
            return Response.Error("INVALID_PARAMETERS", new { reason = "Parameters object was null." });

        if (!TryParseScope(parameters.Scope, out var scope, out string scopeError))
            return Response.Error("INVALID_SCOPE", new { field = nameof(parameters.Scope), reason = scopeError });

        if (EditorApplication.isPlaying)
            return Response.Error("PLAY_MODE", new { reason = "Material conversion is editor-only. Exit Play Mode first." });

        if (!GraphicsSettings.isScriptableRenderPipelineEnabled) {
            return Response.Error("NO_SRP", new {
                reason = "No Scriptable Render Pipeline is assigned.",
                hint = "Assign a URP or HDRP asset under Edit > Project Settings > Graphics."
            });
        }

        if (scope == MaterialConversionScope.Selected) {
            var validation = ValidateSelection();
            if (validation != null)
                return validation;
        }

        string menuPath = scope == MaterialConversionScope.All ? MenuPathAll : MenuPathSelected;
        bool executed = EditorApplication.ExecuteMenuItem(menuPath);

        if (!executed) {
            return Response.Error("MENU_ITEM_FAILED", new {
                menuPath,
                scope = scope.ToString(),
                hint = "Confirm the menu item exists and preconditions are met (e.g. materials selected)."
            });
        }

        return Response.Success($"Material conversion started via menu: {menuPath}", new {
            scope = scope.ToString(),
            menuPath,
            renderPipeline = GraphicsSettings.currentRenderPipeline?.GetType().Name
                             ?? GraphicsSettings.defaultRenderPipeline?.GetType().Name
        });
    }

    static bool TryParseScope(string raw, out MaterialConversionScope scope, out string error) {
        scope = MaterialConversionScope.All;
        error = null;

        if (string.IsNullOrWhiteSpace(raw)) {
            error = "Scope is required. Use 'All' or 'Selected'.";
            return false;
        }

        if (!System.Enum.TryParse(raw, ignoreCase: true, out scope)) {
            error = $"Unknown scope '{raw}'. Use 'All' or 'Selected'.";
            return false;
        }

        return true;
    }

    static object ValidateSelection() {
        if (Selection.objects == null || Selection.objects.Length == 0) {
            return Response.Error("NO_SELECTION", new {
                reason = "Scope is 'Selected' but nothing is selected.",
                hint = "Select one or more Material assets in the Project window."
            });
        }

        for (int i = 0; i < Selection.objects.Length; i++) {
            if (Selection.objects[i] is not Material) {
                return Response.Error("INVALID_SELECTION", new {
                    reason = "Scope is 'Selected' but the selection includes non-Material objects.",
                    selectedType = Selection.objects[i]?.GetType().Name,
                    hint = "Select only Material assets."
                });
            }
        }

        return null;
    }
}