Addon Development

Addon Development in Godot 4.3+

Editor plugins extend the Godot editor itself: custom node types, inspector panels, dock widgets, 3D gizmos, and toolbar buttons. All examples target Godot 4.3+ with no deprecated APIs.

Related skills: resource-pattern for custom Resource editors, godot-ui for editor panel UI, csharp-godot for C# plugin development.

1. Plugin Structure

Every plugin lives inside addons/ at the project root. Godot discovers plugins by scanning for plugin.cfg files.

res://
└── addons/
    └── my_plugin/
        ├── plugin.cfg          # required — plugin metadata
        ├── plugin.gd           # main EditorPlugin script (named in plugin.cfg)
        ├── my_inspector.gd     # optional — EditorInspectorPlugin
        ├── my_dock.tscn        # optional — dock panel scene
        └── icons/
            └── my_node.svg     # optional — custom node icons

plugin.cfg is a plain INI file. Godot reads it when scanning addons/. The script key must point to the main plugin script relative to the plugin folder.

Enable the plugin: Project → Project Settings → Plugins → tick the checkbox next to your plugin name.

2. @tool Annotation

@tool makes a GDScript (or its C# equivalent) run inside the editor process as well as at runtime. Without it, the script only runs when the game is playing.

GDScript

@tool
extends Sprite2D

# Engine.is_editor_hint() is true when running inside the editor,
# false during a running game. Use it to guard editor-only logic.
func _process(delta: float) -> void:
    if Engine.is_editor_hint():
        # This block runs in the editor viewport — safe to call editor APIs.
        update_configuration_warnings()
    else:
        # Normal game logic here.
        pass


# _get_configuration_warnings() returns an array of strings shown as
# yellow warning icons on the node in the Scene panel.
func _get_configuration_warnings() -> PackedStringArray:
    var warnings := PackedStringArray()
    if texture == null:
        warnings.append("Texture is not set. Assign a Texture2D in the Inspector.")
    return warnings

C#

#if TOOLS
using Godot;

[Tool]
public partial class MyToolSprite : Sprite2D
{
    public override void _Process(double delta)
    {
        if (Engine.IsEditorHint())
        {
            // Editor-only logic — safe to call editor APIs here.
            UpdateConfigurationWarnings();
        }
        else
        {
            // Normal game logic.
        }
    }

    public override string[] _GetConfigurationWarnings()
    {
        if (Texture == null)
            return new[] { "Texture is not set. Assign a Texture2D in the Inspector." };
        return System.Array.Empty<string>();
    }
}
#endif

Wrap C# tool scripts in #if TOOLS / #endif to prevent the class from being included in exported builds. GDScript @tool scripts are excluded from exports automatically.

Key rules:

• Add @tool / [Tool] at the top of every script that needs editor access.
• Always guard runtime-only code with Engine.is_editor_hint() to avoid crashing the editor when processing begins before the scene is fully loaded.
• Call update_configuration_warnings() whenever a property changes that might affect the warning state.

3. EditorPlugin Base

The main plugin script extends EditorPlugin. Godot calls _enter_tree() when the plugin is enabled and _exit_tree() when it is disabled or the project is closed. Everything added in _enter_tree() must be removed in _exit_tree().

GDScript

# plugin.gd
@tool
extends EditorPlugin


func _enter_tree() -> void:
    # Register a custom node type. The editor shows MyNode in the
    # "Add Node" dialog under the chosen base class, with a custom icon.
    add_custom_type(
        "MyNode",                              # name shown in editor
        "Node2D",                              # base class to extend
        preload("res://addons/my_plugin/my_node.gd"),
        preload("res://addons/my_plugin/icons/my_node.svg")
    )

    # Add a menu item to the Project menu (top toolbar).
    add_tool_menu_item("My Plugin Action", _on_tool_menu_item)


func _exit_tree() -> void:
    remove_custom_type("MyNode")
    remove_tool_menu_item("My Plugin Action")


func _on_tool_menu_item() -> void:
    print("My Plugin Action triggered")

C#

// Plugin.cs
#if TOOLS
using Godot;

[Tool]
public partial class MyPlugin : EditorPlugin
{
    public override void _EnterTree()
    {
        AddCustomType(
            "MyNode",
            "Node2D",
            GD.Load<Script>("res://addons/my_plugin/MyNode.cs"),
            GD.Load<Texture2D>("res://addons/my_plugin/icons/my_node.svg")
        );

        AddToolMenuItem("My Plugin Action", new Callable(this, MethodName.OnToolMenuAction));
    }

    public override void _ExitTree()
    {
        RemoveCustomType("MyNode");
        RemoveToolMenuItem("My Plugin Action");
    }

    private void OnToolMenuAction()
    {
        GD.Print("My Plugin Action triggered");
    }
}
#endif

add_custom_type parameters:

add_tool_menu_item adds an entry under Project in the top menu bar. Pass a Callable that takes no arguments.

Unsaved-State & Script Editor Control (Godot 4.7+)

Godot 4.7 adds file-management APIs useful for build/export tooling — check for unsaved work before running an action, or refresh scripts changed by an external tool.

func _run_pre_build_check() -> void:
    var unsaved_scenes := EditorInterface.get_unsaved_scenes()  # PackedStringArray of scene paths
    var script_editor := EditorInterface.get_script_editor()
    var unsaved_files := script_editor.get_unsaved_files()      # PackedStringArray of script paths
    if not unsaved_scenes.is_empty() or not unsaved_files.is_empty():
        push_warning("Unsaved work detected — save before building.")

    script_editor.save_all_scripts()   # saves every open script
    script_editor.reload_open_files()  # re-read files changed outside the editor
    # Closes the tab, discarding unsaved changes; OK or ERR_FILE_NOT_FOUND.
    var err := script_editor.close_file("res://addons/my_plugin/generated.gd")

#if TOOLS
private void RunPreBuildCheck()
{
    string[] unsavedScenes = EditorInterface.Singleton.GetUnsavedScenes();
    var scriptEditor = EditorInterface.Singleton.GetScriptEditor();
    string[] unsavedFiles = scriptEditor.GetUnsavedFiles();
    if (unsavedScenes.Length > 0 || unsavedFiles.Length > 0)
        GD.PushWarning("Unsaved work detected — save before building.");

    scriptEditor.SaveAllScripts();
    scriptEditor.ReloadOpenFiles();
    Error err = scriptEditor.CloseFile("res://addons/my_plugin/Generated.cs");
}
#endif

4. Custom Inspector Plugin

When you want a custom widget for an exported property of a specific type, register an EditorInspectorPlugin from your main EditorPlugin. The inspector plugin overrides _can_handle to opt in and _parse_property (or _parse_begin) to inject custom widgets. Pair with an EditorProperty subclass for the actual UI.

See references/inspector-plugins.md for the full GDScript and C# scaffold (custom inspector + EditorProperty + registration boilerplate).

Godot 4.7+: the static EditorInspector.create_default_inspector(filter_line_edit: LineEdit = null) returns an inspector with the same configuration as the editor's Inspector dock, ready to embed in plugin UIs — pass a LineEdit for live property filtering (see references/inspector-plugins.md). EditorContextMenuPlugin also gains CONTEXT_SLOT_INSPECTOR_PROPERTY in ContextMenuSlot, so context-menu plugins can extend the inspector property right-click menu: _popup_menu() receives [object ID, property name] and the option callback receives the EditorProperty directly.

5. Custom Dock Panel

Add a custom dock to the editor by calling add_control_to_dock(slot, control) from your EditorPlugin._enter_tree. Free the control on _exit_tree. Useful for project-wide tooling UIs (level browser, asset summary, build dashboard).

See references/dock-panels.md for the full GDScript and C# dock scaffold.

6. Custom Resource Editors

EditorResourcePicker lets you constrain a property to a specific Resource subclass with a tooltip and base-type filter. EditorResourcePreviewGenerator provides custom thumbnails for resources in the FileSystem dock and Inspector.

See references/inspector-plugins.md for the full GDScript and C# EditorResourcePicker and EditorResourcePreviewGenerator scaffolds.

7. Gizmos

EditorNode3DGizmoPlugin adds visual handles for 3D nodes in the editor — wireframe shapes, draggable handles, rotation rings. Implement _init (materials), _get_gizmo_name, _has_gizmo, _redraw (draw lines/handles), and _get_handle_value / _set_handle / _commit_handle for interactive editing.

See references/gizmos-deep-dive.md for the full GDScript and C# gizmo plugin (with undo/redo wiring for handle commits).

Godot 4.7+: override _can_commit_handle_on_click() -> bool (returns false if not overridden) to commit a handle action even when the final handle position is the same as the initial one — i.e. on a plain click.

8. Testing Plugins

Toggle the plugin off and on in Project Settings → Plugins to reload it; saving a @tool script hot-reloads automatically, but new class registrations and dock changes need the full cycle. print() / push_warning() / push_error() go to the Output panel. C# plugins must recompile first — Could not find type "Plugin" means the assembly failed to build, so check the MSBuild panel before anything else.

Reload recipes (GDScript + C# PluginReloader), console launch flags, and the lifecycle-gotcha table (orphaned docks, stale custom types, double-registered inspector plugins): references/testing-plugins.md

9. plugin.cfg Format

plugin.cfg is a plain INI file placed at the root of the plugin folder. All fields in the [plugin] section are required except dependencies and installs.

[plugin]

name="My Plugin"
description="Adds MyNode, a custom inspector, and a dock panel to the editor."
author="Your Name"
version="1.0.0"
script="plugin.gd"

Field reference:

Complete example with all optional fields:

[plugin]

name="My Plugin"
description="Adds MyNode, a custom inspector, and a dock panel to the editor."
author="Your Name"
version="1.0.0"
script="plugin.gd"

There are no other standard keys in Godot 4.x plugin.cfg. Dependency management is handled externally (e.g., by the Asset Library or manual installation instructions).

10. Checklist

• addons/<plugin_name>/plugin.cfg exists with name, description, author, version, script
• Main script extends EditorPlugin and is decorated with @tool (GDScript) or [Tool] inside #if TOOLS (C#)
• Everything registered in _enter_tree() is unregistered in _exit_tree()
• Custom node types use add_custom_type / remove_custom_type with a matching icon SVG
• @tool scripts guard editor-only code with Engine.is_editor_hint()
• _get_configuration_warnings() returns non-empty array when node is misconfigured
• Inspector plugins implement _can_handle to avoid handling unintended types
• _parse_property returns true only for properties that need a custom editor
• Dock scenes have a Custom Minimum Size set so the panel is usable at default dock widths
• Dock Control is freed with queue_free() in _exit_tree()
• EditorResourcePreviewGenerator is both added and removed via EditorInterface.get_resource_previewer()
• Gizmo plugin implements _commit_handle with get_undo_redo() so handle drags are undoable
• Plugin tested by full disable/enable cycle after each structural change
• push_error() used instead of silent failures in all _enter_tree setup paths
• C# plugin scripts wrapped in #if TOOLS / #endif