Unity Mark Unused Assets

MarkUnused.cs

using System;
using System.Collections.Generic;
using System.Linq;
using System.Reflection;
using UnityEditor;
using UnityEngine;

public class MarkUnused
{
    private const string UnusedLabel = "Unused"; // All unused assets will be tagged with this label

    [MenuItem("Assets/Mark Unused Assets", false, 59)]
    private static void MarkUnusedAssets()
    {
        EditorUtility.DisplayProgressBar("Searching for unused assets", "Finding dependencies", 0.1f);

        // find all scene GUIDs
        var allScenes = AssetDatabase.FindAssets("t:scene");
        // translate GUIDs to paths
        var allScenesPaths = allScenes.Select(AssetDatabase.GUIDToAssetPath).ToArray();
        // gather all dependencies (once only)
        var dependencies = new HashSet<string>(AssetDatabase.GetDependencies(allScenesPaths));

        // list all types you are interested in
        var allItems = new List<string>(AssetDatabase.FindAssets("t:Sprite t:VideoClip t:AudioClip"));

        var unusedCounter = 0;
        var progress = 0;
        foreach (var guid in allItems)
        {
            var path = AssetDatabase.GUIDToAssetPath(guid);
            var loadedAsset = AssetDatabase.LoadMainAssetAtPath(path);
            var isUsed = dependencies.Contains(path);

            LabelAsset(loadedAsset, isUsed);

            if (!isUsed)
            {
                unusedCounter++;
            }

            progress++;
            EditorUtility.DisplayProgressBar("Searching for unused assets", "Labeling assets", (float) progress / allItems.Count * 0.9f + 0.1f);
        }

        AssetDatabase.Refresh();
        Debug.Log("Found " + unusedCounter + " unused assets");

        // Set search in Project browser to show all unused assets
        try
        {
            var projectBrowserType = Type.GetType("UnityEditor.ProjectBrowser,UnityEditor");
            var window = EditorWindow.GetWindow(projectBrowserType);
            MethodInfo setSearchMethodInfo = projectBrowserType.GetMethod("SetSearch",
                BindingFlags.NonPublic | BindingFlags.Public | BindingFlags.Instance,
                null, new[] {typeof(string)}, null);
            setSearchMethodInfo.Invoke(window, new object[] {"l:" + UnusedLabel});
        }
        catch
        {
            // this might possibly break in the future
        }

        EditorUtility.ClearProgressBar();
    }

    // Labels asset as unused or removes the label if used
    private static void LabelAsset(UnityEngine.Object asset, bool isUsed)
    {
        var labelList = new List<string>(AssetDatabase.GetLabels(asset));
        bool changed = false;
        if (labelList.Contains(UnusedLabel) && isUsed)
        {
            labelList.Remove(UnusedLabel);
            changed = true;
        }
        else if (!labelList.Contains(UnusedLabel) && !isUsed)
        {
            labelList.Add(UnusedLabel);
            changed = true;
        }

        if (changed)
        {
            AssetDatabase.SetLabels(asset, labelList.ToArray());
            EditorUtility.SetDirty(asset);
        }
    }
}

Add this file to an Editor folder to add the ability to tag all unused assets in your project. It can run a long time if you have a lot of unused assets.