Edit Scene

Guide for creating and editing Unity scene files in Unity projects.

Rules

• Do not directly Edit or Write .unity or .prefab files. Instead, write an editor script under Assets/Editor/ and execute it in Unity to create or update the scene or prefab — those carry GameObject/Prefab-instance structure that is unsafe to author by hand.
• Editor scripts must always end with EditorSceneManager.SaveScene (or PrefabUtility.SaveAsPrefabAsset for prefabs). Treat "no dirty scenes/assets at script exit" as a hard postcondition.
• Scene: EditorSceneManager.SaveScene(scene, path) (new) or EditorSceneManager.SaveScene(scene) (existing). The return value is true on success.
• Prefab: PrefabUtility.SaveAsPrefabAsset(go, path). When editing via LoadPrefabContents, always pair with SaveAsPrefabAsset → UnloadPrefabContents.
• When the script also creates side-effect assets (Materials, ScriptableObjects, etc.), call AssetDatabase.SaveAssets() after the per-object saves to flush pending writes.
• Before running an editor script, check if the editor is in Play Mode using the unity_play_control tool. If it is, stop it first — Play Mode may skip recompilation, leaving stale code active.
• After modifying code, confirm compilation success using the get_unity_compilation_result tool before running.
• To determine which assembly an editor script belongs to, run ${CLAUDE_SKILL_DIR}/scripts/resolve-assembly.sh . It walks up directories to find the nearest .asmdef; if none is found, it falls back to Assembly-CSharp-Editor (path contains /Editor/) or Assembly-CSharp.
• Prefer the run_method_in_unity tool (MCP Server Extension for Unity) for execution. Define a public static method in the script (adding [MenuItem("Tools/...")] is optional) and invoke it directly via run_method_in_unity. Only fall back to execute_run_configuration or other alternatives when run_method_in_unity is unavailable.
• For uGUI buttons and text, use the legacy variants (UnityEngine.UI.Button / UnityEngine.UI.Text). Do not use TextMeshPro unless the user explicitly requests it.
• Apply context-menu-equivalent defaults when creating uGUI components (see Resources below).

Gotchas

• Never call two Unity Editor tools in parallel. unity_play_control, get_unity_compilation_result, run_method_in_unity, and run_unity_tests must be called strictly one at a time — always wait for each call to return before making the next one. Calling them concurrently causes domain-reload conflicts that result in "canceled" or "did not connect within 30 seconds" errors.
• When a Unity Editor tool returns error or canceled, wait 10 seconds before retrying. Domain reload typically takes several seconds; immediate retry hits the same in-flight reload and fails again. Do not switch tools in the meantime (e.g., calling unity_play_control to verify state) — that just compounds the multiplexed calls. If the same tool returns error or canceled on two consecutive attempts (with the 10-second wait between them), stop and consult the user instead of retrying further.
• .meta files follow an asymmetric commit rule. Never create them manually — Unity generates them automatically. Scene/prefab files (.unity, .prefab) and their referenced assets (materials, SOs, etc.) must be committed (required for GUID resolution); editor scripts (Assets/Editor/*.cs) and their .meta must not be committed — orphaned metas break the other checkout if the script is absent. Do not delete them; leave them for the user to remove manually. Do not add them to .gitignore; the user excludes them at commit time.

Scene lifecycle

• New scene: First determine whether the scene will be loaded additively or as a single scene, then choose the setup accordingly.
• Additive (LoadSceneMode.Additive): EditorSceneManager.NewScene(NewSceneSetup.EmptyScene, NewSceneMode.Single) — no camera or light needed.
• Single (LoadSceneMode.Single): EditorSceneManager.NewScene(NewSceneSetup.DefaultGameObjects, NewSceneMode.Single) — Main Camera and Directional Light are included automatically; do not add a camera manually.
• In both cases, place additional GameObjects via ObjectFactory.CreateGameObject and save with EditorSceneManager.SaveScene(scene, "Assets/YourFeature/Scenes/XxxScene.unity").
• Edit existing scene: EditorSceneManager.OpenScene(path, OpenSceneMode.Single) → make changes → EditorSceneManager.SaveScene(scene).
• New prefab: build the GameObject hierarchy in memory, then save with PrefabUtility.SaveAsPrefabAsset(go, "Assets/YourFeature/Prefabs/XxxPrefab.prefab").
• Edit existing prefab: open with PrefabUtility.LoadPrefabContents(path) → modify → PrefabUtility.SaveAsPrefabAsset(root, path) → PrefabUtility.UnloadPrefabContents(root).
• Use ObjectFactory.CreateGameObject / ObjectFactory.AddComponent so Undo history and Presets are applied automatically.
• Parent child objects with transform.SetParent(parent, worldPositionStays: false).

Resources

• Before writing or modifying any editor script that creates or manipulates uGUI components: Read ${CLAUDE_SKILL_DIR}/resources/ugui.md

Troubleshooting

• The run_method_in_unity tool is not available or fails with a connection error: Read ${CLAUDE_SKILL_DIR}/resources/troubleshooting-run-method-in-unity.md

Source & license

This open-source skill is cataloged on AgentStack and links to its original source — we do not rehost the code.

• Author: nowsprinting
• Source: nowsprinting/claude-code-settings-for-unity
• License: Unlicense
• Homepage: https://www.nowsprinting.com/entry/2025/07/05/053055

Install and usage instructions live in the source repository linked above.