Unity-Technologies/UnityCsReference · error · ArgumentException

Given path is not valid: '{path}'

Error message

Given path is not valid: '{path}'

What it means

ValidatePath throws ArgumentException when Paths.IsValidAssetPath(path, ".prefab") fails — the path is not a syntactically valid prefab asset path. This covers wrong/missing extension, invalid characters, or a path that does not conform to Unity's asset path rules.

Source

Thrown at Editor/Mono/Prefabs/PrefabUtility.cs:2044

            string path = AssetDatabase.GetAssetPath(asset);
            if (String.IsNullOrEmpty(path))
                throw new ArgumentException("Can't save a Prefab instance");

            var root = asset.transform.root.gameObject;
            if (root != asset)
                throw new ArgumentException("GameObject to save Prefab from must be a Prefab root");

            return SavePrefabAsset_Internal(root, out savedSuccessfully);
        }

        internal static void ValidatePath(GameObject instanceRoot, string path)
        {
            if (String.IsNullOrEmpty(path))
                throw new ArgumentNullException("path is null or empty");

            if (!Paths.IsValidAssetPath(path, ".prefab"))
                throw new ArgumentException("Given path is not valid: '" + path + "'");

            if (Directory.Exists(path))
                throw new ArgumentException("Overwriting a folder with an Asset is not allowed: '" + path + "'");

            string directory = Path.GetDirectoryName(path);

            // We allow relative paths outside the Assets folder so we do not throw if isValidAssetFolder is false
            bool isRootFolder = false;
            bool isImmutableFolder = false;
            bool isValidAssetFolder = AssetDatabase.TryGetAssetFolderInfo(directory, out isRootFolder, out isImmutableFolder);

            if (isValidAssetFolder && isImmutableFolder)
                throw new ArgumentException("Saving Prefab to immutable folder is not allowed: '" + path + "'");

            if (directory.Length > 0 && !Directory.Exists(directory))
                throw new ArgumentException("Given path does not exist: '" + path + "'");

            if (isValidAssetFolder)

View on GitHub (pinned to 225b0fbdb5)

Solutions

1. Ensure the path is relative to the project folder and ends with .prefab.
2. Normalize separators to forward slashes and use AssetDatabase.GenerateUniqueAssetPath for a valid base.
3. Verify with Paths.IsValidAssetPath(path, ".prefab") before calling when accessible, or check extension and characters manually.

Example fix

// before
PrefabUtility.SaveAsPrefabAsset(instance, @"C:\\prefabs\\MyPrefab");

// after
string path = "Assets/Prefabs/MyPrefab.prefab";
path = AssetDatabase.GenerateUniqueAssetPath(path);
PrefabUtility.SaveAsPrefabAsset(instance, path);

if (string.IsNullOrEmpty(path) || !path.EndsWith(".prefab")) return;
path = path.Replace('\\', '/');

static bool IsValidPrefabPath(string path) =>
    !string.IsNullOrEmpty(path) && path.EndsWith(".prefab")
    && path.IndexOfAny(Path.GetInvalidPathChars()) < 0;

When it happens

Trigger: Passing a path without the .prefab extension, with backslashes on a project that expects forward slashes, with illegal characters, or an absolute path instead of a project-relative one.

Common situations: Mixing System.IO.Path separators with Unity asset paths; forgetting the extension; passing an absolute OS path; copy-pasting a path with stray characters.

Related errors

• path is null or empty
• Incorrect file extension: {prefabAssetPath}. Must be '.prefa
• guid
• prefabInstance
• Provided GameObject is not a Prefab instance

AI-assisted analysis of Unity-Technologies/UnityCsReference@225b0fbdb5 (2026-08-13). Data as JSON: /api/errors/93d67ee7ea0042b6. Report an issue: GitHub.