Fix: Godot C# Tool Script Hot Reload Loses State

A custom [Tool] node builds a procedural mesh in the editor. After every C# rebuild, the configured parameters vanish — hot reload didn’t preserve the plain fields.

Plain Fields Don't Survive

On rebuild, Godot reconstructs the managed object. Only data Godot knows how to serialize — exported properties — is restored. Plain C# fields revert to defaults.

Use Exported Properties for State

[Tool]
public partial class ProcMesh : Node3D
{
    [Export] public int Segments { get; set; } = 8;
    [Export] public float Radius { get; set; } = 1.0f;

    // transient — OK to lose, rebuilt below
    private Mesh _cachedMesh;
}

Anything the user configures must be [Export]. Transient caches can be plain fields — just rebuild them.

Rebuild Caches in _Ready / _EnterTree

public override void _Ready()
{
    if (Engine.IsEditorHint())
        RebuildMesh();   // regenerate from exported params
}

_Ready runs after a hot reload reconstructs the node. Regenerate transient data from the (preserved) exported properties.

NotifyPropertyListChanged

If your tool changes the property list dynamically, call NotifyPropertyListChanged() after a reload so the Inspector refreshes.

Verifying

Configure the tool node, edit the C# script, rebuild. Exported parameters survive; the mesh regenerates from them. No lost configuration.

“Hot reload only keeps what Godot serializes. Exported properties survive; plain fields don’t.”

Treat _Ready in a tool script as ‘reconstruct everything transient’ — it runs both on scene open and after every reload.