{
  "type": "propertyEditorUi",
  "alias": "My.PropertyEditorUi.Custom",
  "name": "My Custom Editor",
  "element": "/App_Plugins/MyEditor/editor.js",
  "meta": {
    "propertyEditorSchemaAlias": "Umbraco.Plain.String"
  }
}

using Umbraco.Cms.Core.IO;
using Umbraco.Cms.Core.PropertyEditors;
using Umbraco.Cms.Core.Services;

namespace MyPackage.PropertyEditors;

[DataEditor(
    alias: "My.PropertyEditor.Custom",
    name: "My Custom Editor",
    view: "~/App_Plugins/MyEditor/editor.html")]
public class MyPropertyEditor : DataEditor
{
    private readonly IIOHelper _ioHelper;
    private readonly IEditorConfigurationParser _editorConfigurationParser;

    public MyPropertyEditor(
        IDataValueEditorFactory dataValueEditorFactory,
        IIOHelper ioHelper,
        IEditorConfigurationParser editorConfigurationParser)
        : base(dataValueEditorFactory)
    {
        _ioHelper = ioHelper;
        _editorConfigurationParser = editorConfigurationParser;
        SupportsReadOnly = true;
    }

    protected override IConfigurationEditor CreateConfigurationEditor() =>
        new MyConfigurationEditor(_ioHelper, _editorConfigurationParser);
}

using Umbraco.Cms.Core.IO;
using Umbraco.Cms.Core.PropertyEditors;
using Umbraco.Cms.Core.Services;

namespace MyPackage.PropertyEditors;

public class MyConfigurationEditor : ConfigurationEditor<MyConfiguration>
{
    public MyConfigurationEditor(
        IIOHelper ioHelper,
        IEditorConfigurationParser editorConfigurationParser)
        : base(ioHelper, editorConfigurationParser)
    {
    }
}

public class MyConfiguration
{
    [ConfigurationField("maxItems", "Maximum Items", "number")]
    public int MaxItems { get; set; } = 10;

    [ConfigurationField("allowNull", "Allow Empty", "boolean")]
    public bool AllowNull { get; set; } = true;
}

using Umbraco.Cms.Core.Models.PublishedContent;
using Umbraco.Cms.Core.PropertyEditors;

namespace MyPackage.PropertyEditors;

public class MyValueConverter : PropertyValueConverterBase
{
    public override bool IsConverter(IPublishedPropertyType propertyType)
        => propertyType.EditorAlias == "My.PropertyEditor.Custom";

    public override Type GetPropertyValueType(IPublishedPropertyType propertyType)
        => typeof(MyModel);

    public override object? ConvertSourceToIntermediate(
        IPublishedElement owner,
        IPublishedPropertyType propertyType,
        object? source,
        bool preview)
    {
        if (source is string json && !string.IsNullOrEmpty(json))
        {
            return JsonSerializer.Deserialize<MyModel>(json);
        }
        return null;
    }
}