diff --git a/src/Server/ZB.MOM.WW.OtOpcUa.AdminUI/Components/Shared/Uns/TagEditors/ModbusTagConfigEditor.razor b/src/Server/ZB.MOM.WW.OtOpcUa.AdminUI/Components/Shared/Uns/TagEditors/ModbusTagConfigEditor.razor
new file mode 100644
index 00000000..bcaa0533
--- /dev/null
+++ b/src/Server/ZB.MOM.WW.OtOpcUa.AdminUI/Components/Shared/Uns/TagEditors/ModbusTagConfigEditor.razor
@@ -0,0 +1,52 @@
+@using ZB.MOM.WW.OtOpcUa.AdminUI.Uns.TagEditors
+@using ZB.MOM.WW.OtOpcUa.Driver.Modbus
+
+<div class="row g-2">
+    <div class="col-md-4"><label class="form-label">Region</label>
+        <select class="form-select form-select-sm" value="@_m.Region" @onchange="@(e => Update(() => _m.Region = ParseEnum(e.Value, ModbusRegion.HoldingRegisters)))">
+            @foreach (var v in Enum.GetValues<ModbusRegion>()) { <option value="@v">@v</option> }
+        </select></div>
+    <div class="col-md-2"><label class="form-label">Address</label>
+        <input type="number" class="form-control form-control-sm" value="@_m.Address" @onchange="@(e => Update(() => _m.Address = ParseInt(e.Value)))" /></div>
+    <div class="col-md-3"><label class="form-label">Data type</label>
+        <select class="form-select form-select-sm" value="@_m.DataType" @onchange="@(e => Update(() => _m.DataType = ParseEnum(e.Value, ModbusDataType.Int16)))">
+            @foreach (var v in Enum.GetValues<ModbusDataType>()) { <option value="@v">@v</option> }
+        </select></div>
+    <div class="col-md-3"><label class="form-label">Byte order</label>
+        <select class="form-select form-select-sm" value="@_m.ByteOrder" @onchange="@(e => Update(() => _m.ByteOrder = ParseEnum(e.Value, ModbusByteOrder.BigEndian)))">
+            @foreach (var v in Enum.GetValues<ModbusByteOrder>()) { <option value="@v">@v</option> }
+        </select></div>
+    <div class="col-md-2"><label class="form-label">Bit index</label>
+        <input type="number" class="form-control form-control-sm" value="@_m.BitIndex" @onchange="@(e => Update(() => _m.BitIndex = ParseInt(e.Value)))" /></div>
+    <div class="col-md-2"><label class="form-label">String len</label>
+        <input type="number" class="form-control form-control-sm" value="@_m.StringLength" @onchange="@(e => Update(() => _m.StringLength = ParseInt(e.Value)))" /></div>
+</div>
+
+@code {
+    [Parameter] public string? ConfigJson { get; set; }
+    [Parameter] public EventCallback<string> ConfigJsonChanged { get; set; }
+
+    private ModbusTagConfigModel _m = new();
+    private string? _lastConfigJson;
+
+    // Re-parse only when the incoming JSON actually changes, so an unrelated parent re-render
+    // (Blazor Server live-status pushes do this) can't reset the user's in-progress edits.
+    protected override void OnParametersSet()
+    {
+        if (ConfigJson == _lastConfigJson) { return; }
+        _lastConfigJson = ConfigJson;
+        _m = ModbusTagConfigModel.FromJson(ConfigJson);
+    }
+
+    private static int ParseInt(object? v, int fallback = 0) => int.TryParse(v?.ToString(), out var i) ? i : fallback;
+
+    // TryParse so a bad/empty change value can never throw into the Blazor circuit — it falls back.
+    private static TEnum ParseEnum<TEnum>(object? v, TEnum fallback) where TEnum : struct, Enum
+        => Enum.TryParse<TEnum>(v?.ToString(), out var r) ? r : fallback;
+
+    private async Task Update(Action apply)
+    {
+        apply();
+        await ConfigJsonChanged.InvokeAsync(_m.ToJson());
+    }
+}
diff --git a/src/Server/ZB.MOM.WW.OtOpcUa.AdminUI/Uns/TagEditors/ModbusTagConfigModel.cs b/src/Server/ZB.MOM.WW.OtOpcUa.AdminUI/Uns/TagEditors/ModbusTagConfigModel.cs
new file mode 100644
index 00000000..9fb33ded
--- /dev/null
+++ b/src/Server/ZB.MOM.WW.OtOpcUa.AdminUI/Uns/TagEditors/ModbusTagConfigModel.cs
@@ -0,0 +1,62 @@
+using System.Text.Json.Nodes;
+using ZB.MOM.WW.OtOpcUa.Driver.Modbus;
+
+namespace ZB.MOM.WW.OtOpcUa.AdminUI.Uns.TagEditors;
+
+/// <summary>Typed working model for a Modbus tag's TagConfig JSON (the driver-specific addressing/encoding
+/// fields; name/writable live on the Tag entity). Preserves unrecognised JSON keys across a load→save.</summary>
+public sealed class ModbusTagConfigModel
+{
+    /// <summary>Register region (HoldingRegisters/InputRegisters/Coils/DiscreteInputs).</summary>
+    public ModbusRegion Region { get; set; } = ModbusRegion.HoldingRegisters;
+
+    /// <summary>Starting register/coil address.</summary>
+    public int Address { get; set; }
+
+    /// <summary>Wire value type the register block decodes to.</summary>
+    public ModbusDataType DataType { get; set; } = ModbusDataType.Int16;
+
+    /// <summary>Word/byte ordering for multi-register values.</summary>
+    public ModbusByteOrder ByteOrder { get; set; } = ModbusByteOrder.BigEndian;
+
+    /// <summary>Bit index (0-15) for BitInRegister tags.</summary>
+    public int BitIndex { get; set; }
+
+    /// <summary>String length in characters for String tags.</summary>
+    public int StringLength { get; set; }
+
+    private JsonObject _bag = new();
+
+    /// <summary>Loads a model from a TagConfig JSON string, defaulting any absent field and retaining
+    /// every original key (so fields this editor doesn't expose survive a load→save).</summary>
+    public static ModbusTagConfigModel FromJson(string? json)
+    {
+        var o = TagConfigJson.ParseOrNew(json);
+        return new ModbusTagConfigModel
+        {
+            Region = TagConfigJson.GetEnum(o, "region", ModbusRegion.HoldingRegisters),
+            Address = TagConfigJson.GetInt(o, "address"),
+            DataType = TagConfigJson.GetEnum(o, "dataType", ModbusDataType.Int16),
+            ByteOrder = TagConfigJson.GetEnum(o, "byteOrder", ModbusByteOrder.BigEndian),
+            BitIndex = TagConfigJson.GetInt(o, "bitIndex"),
+            StringLength = TagConfigJson.GetInt(o, "stringLength"),
+            _bag = o,
+        };
+    }
+
+    /// <summary>Serialises this model back to a TagConfig JSON string, writing the six exposed fields
+    /// (enums as their name strings) over the preserved key bag.</summary>
+    public string ToJson()
+    {
+        TagConfigJson.Set(_bag, "region", Region);
+        TagConfigJson.Set(_bag, "address", Address);
+        TagConfigJson.Set(_bag, "dataType", DataType);
+        TagConfigJson.Set(_bag, "byteOrder", ByteOrder);
+        TagConfigJson.Set(_bag, "bitIndex", BitIndex);
+        TagConfigJson.Set(_bag, "stringLength", StringLength);
+        return TagConfigJson.Serialize(_bag);
+    }
+
+    /// <summary>Validation hook; returns an error message or null when the model is valid.</summary>
+    public string? Validate() => null;
+}
diff --git a/src/Server/ZB.MOM.WW.OtOpcUa.AdminUI/Uns/TagEditors/TagConfigEditorMap.cs b/src/Server/ZB.MOM.WW.OtOpcUa.AdminUI/Uns/TagEditors/TagConfigEditorMap.cs
index e754f649..6ace4b30 100644
--- a/src/Server/ZB.MOM.WW.OtOpcUa.AdminUI/Uns/TagEditors/TagConfigEditorMap.cs
+++ b/src/Server/ZB.MOM.WW.OtOpcUa.AdminUI/Uns/TagEditors/TagConfigEditorMap.cs
@@ -10,8 +10,8 @@ public static class TagConfigEditorMap
     private static readonly IReadOnlyDictionary<string, Type> Map =
         new Dictionary<string, Type>(StringComparer.OrdinalIgnoreCase)
         {
-            // Editors registered by later tasks, e.g.:
-            // ["ModbusTcp"] = typeof(Components.Shared.Uns.TagEditors.ModbusTagConfigEditor),
+            ["ModbusTcp"] = typeof(Components.Shared.Uns.TagEditors.ModbusTagConfigEditor),
+            // Further editors registered by later tasks, e.g. ["AbCip"] = typeof(...).
         };
 
     /// <summary>Returns the editor component type for a driver type, or null if none is registered.</summary>
diff --git a/tests/Server/ZB.MOM.WW.OtOpcUa.AdminUI.Tests/Uns/ModbusTagConfigModelTests.cs b/tests/Server/ZB.MOM.WW.OtOpcUa.AdminUI.Tests/Uns/ModbusTagConfigModelTests.cs
new file mode 100644
index 00000000..5fe913c3
--- /dev/null
+++ b/tests/Server/ZB.MOM.WW.OtOpcUa.AdminUI.Tests/Uns/ModbusTagConfigModelTests.cs
@@ -0,0 +1,92 @@
+using Shouldly;
+using Xunit;
+using ZB.MOM.WW.OtOpcUa.AdminUI.Uns.TagEditors;
+using ZB.MOM.WW.OtOpcUa.Driver.Modbus;
+
+namespace ZB.MOM.WW.OtOpcUa.AdminUI.Tests.Uns;
+
+public sealed class ModbusTagConfigModelTests
+{
+    [Theory]
+    [InlineData(null)]
+    [InlineData("")]
+    [InlineData("   ")]
+    [InlineData("{}")]
+    public void FromJson_returns_defaults_for_empty_input(string? json)
+    {
+        var m = ModbusTagConfigModel.FromJson(json);
+
+        m.Region.ShouldBe(ModbusRegion.HoldingRegisters);
+        m.Address.ShouldBe(0);
+        m.DataType.ShouldBe(ModbusDataType.Int16);
+        m.ByteOrder.ShouldBe(ModbusByteOrder.BigEndian);
+        m.BitIndex.ShouldBe(0);
+        m.StringLength.ShouldBe(0);
+    }
+
+    [Fact]
+    public void Round_trip_preserves_all_six_fields()
+    {
+        var m = new ModbusTagConfigModel
+        {
+            Region = ModbusRegion.InputRegisters,
+            Address = 40001,
+            DataType = ModbusDataType.Float32,
+            ByteOrder = ModbusByteOrder.WordSwap,
+            BitIndex = 3,
+            StringLength = 16,
+        };
+
+        var json = m.ToJson();
+        var m2 = ModbusTagConfigModel.FromJson(json);
+
+        m2.Region.ShouldBe(ModbusRegion.InputRegisters);
+        m2.Address.ShouldBe(40001);
+        m2.DataType.ShouldBe(ModbusDataType.Float32);
+        m2.ByteOrder.ShouldBe(ModbusByteOrder.WordSwap);
+        m2.BitIndex.ShouldBe(3);
+        m2.StringLength.ShouldBe(16);
+    }
+
+    [Fact]
+    public void ToJson_emits_camelCase_keys_with_enum_names()
+    {
+        var m = new ModbusTagConfigModel
+        {
+            Region = ModbusRegion.HoldingRegisters,
+            Address = 100,
+            DataType = ModbusDataType.Int16,
+            ByteOrder = ModbusByteOrder.BigEndian,
+            BitIndex = 0,
+            StringLength = 0,
+        };
+
+        var json = m.ToJson();
+
+        json.ShouldContain("\"region\":\"HoldingRegisters\"");
+        json.ShouldContain("\"dataType\":\"Int16\"");
+        json.ShouldContain("\"byteOrder\":\"BigEndian\"");
+        json.ShouldContain("\"address\":100");
+        json.ShouldContain("\"bitIndex\":0");
+        json.ShouldContain("\"stringLength\":0");
+    }
+
+    [Fact]
+    public void FromJson_then_ToJson_preserves_unknown_keys()
+    {
+        var json = ModbusTagConfigModel
+            .FromJson("""{"region":"InputRegisters","addressString":"40001:F"}""")
+            .ToJson();
+
+        json.ShouldContain("addressString");
+        json.ShouldContain("40001:F");
+        // and the exposed field still round-trips
+        json.ShouldContain("\"region\":\"InputRegisters\"");
+    }
+
+    [Fact]
+    public void Validate_returns_null_for_default_model()
+    {
+        new ModbusTagConfigModel().Validate().ShouldBeNull();
+    }
+}