Why does my [Tool] script hang the editor when I save?

Tool scripts run in the editor too. Heavy work in _Process or _Notification (NOTIFICATION_EDITOR_PRE_SAVE) blocks the editor. Guard with Engine.IsEditorHint and skip the heavy path during save.

Engine.IsEditorHint returns true inside the editor (including for tool scripts), false in running games. Branch on it to limit editor-time work.

Should I unsubscribe events on _ExitTree?

Yes — tool scripts can hold references to scene-tree handlers that survive across edits. Unsubscribe in _ExitTree to avoid stale callbacks during editor save/reload cycles.

Fix: Godot 4 C# [Tool] Script Hangs Editor on Save

Quick answer: Branch on Engine.IsEditorHint in any heavy method. Avoid running game logic in the editor. Unsubscribe from events in _ExitTree to avoid stale handlers across editor reloads.

Editor freezes for seconds whenever you save the scene. A [Tool] script’s _Process is running pathfinding or simulation while the editor expects fast UI.

The Symptom

Editor lags or hangs after script changes or scene save. Game runs fine. Removing [Tool] removes the hang but loses editor preview.

The Fix

[Tool]
public partial class PathPreview : Node3D
{
    public override void _Process(double dt)
    {
        if (Engine.IsEditorHint)
        {
            // only do cheap work in the editor
            DrawPreview();
        }
        else
        {
            // full game logic at runtime
            RunSimulation(dt);
        }
    }
}

Branch on IsEditorHint. Editor preview stays light; runtime gets the full sim.

Editor-Only Code

public override void _Notification(int what)
{
    if (what == NotificationEditorPreSave && Engine.IsEditorHint)
    {
        // pre-save tasks: regenerate cached preview, etc.
    }
}

Verifying

Save the scene. Editor should respond instantly. Profile via Editor → Debugger → Frame Time during save to identify remaining hot spots.

“Branch on IsEditorHint. Skip heavy at edit time.”

Related Issues

For C# disposed wrapper, see disposed wrapper. For C# task background, see await background.

IsEditorHint guards. Editor breathes.