diff --git a/src/DynamoCore/Graph/Nodes/IValueSchemaProvider.cs b/src/DynamoCore/Graph/Nodes/IValueSchemaProvider.cs
new file mode 100644
index 00000000000..c92df8e4e25
--- /dev/null
+++ b/src/DynamoCore/Graph/Nodes/IValueSchemaProvider.cs
@@ -0,0 +1,22 @@
+namespace Dynamo.Graph.Nodes
+{
+    /// <summary>
+    /// Implemented by NodeModels that can describe their value type
+    /// for external consumers (DynamoPlayer, MCP, etc.).
+    /// Returns a canonical Forge Data Schema type identifier and list context.
+    /// </summary>
+    public interface IValueSchemaProvider
+    {
+        /// <summary>
+        /// Canonical type identifier in Forge Data Schema format.
+        /// Examples: "autodesk.math:point3d-1.0.0", "String", "Float64".
+        /// Returns null if the type is unknown or not yet determined.
+        /// </summary>
+        string ValueTypeId { get; }
+
+        /// <summary>
+        /// Whether the value is a list (array) of the declared type.
+        /// </summary>
+        bool IsListValue { get; }
+    }
+}
diff --git a/src/DynamoCore/PublicAPI.Unshipped.txt b/src/DynamoCore/PublicAPI.Unshipped.txt
index 475a38b3c81..fd19c94b62b 100644
--- a/src/DynamoCore/PublicAPI.Unshipped.txt
+++ b/src/DynamoCore/PublicAPI.Unshipped.txt
@@ -1,3 +1,6 @@
+Dynamo.Graph.Nodes.IValueSchemaProvider
+Dynamo.Graph.Nodes.IValueSchemaProvider.IsListValue.get -> bool
+Dynamo.Graph.Nodes.IValueSchemaProvider.ValueTypeId.get -> string
 Dynamo.Models.DynamoModel.DefaultStartConfiguration.EnableUnTrustedLocationsNotifications.get -> bool
 Dynamo.Models.DynamoModel.DefaultStartConfiguration.EnableUnTrustedLocationsNotifications.set -> void
 Dynamo.Models.DynamoModel.IStartConfiguration.EnableUnTrustedLocationsNotifications.get -> bool
diff --git a/src/Libraries/CoreNodeModels/DefineData.cs b/src/Libraries/CoreNodeModels/DefineData.cs
index 1703a43f901..375bf6b7f7c 100644
--- a/src/Libraries/CoreNodeModels/DefineData.cs
+++ b/src/Libraries/CoreNodeModels/DefineData.cs
@@ -25,8 +25,25 @@ namespace CoreNodeModels
     [OutPortDescriptions(typeof(Properties.Resources), nameof(Properties.Resources.DefineDataOutputTooltip))]
     [IsDesignScriptCompatible]
     [AlsoKnownAs("Data.DefineData")]
-    public class DefineData : DSDropDownBase
+    public class DefineData : DSDropDownBase, IValueSchemaProvider
     {
+        /// <inheritdoc/>
+        [JsonIgnore]
+        public string ValueTypeId
+        {
+            get
+            {
+                if (SelectedIndex < 0 || SelectedIndex >= Items.Count)
+                    return SelectedString;
+
+                return (Items[SelectedIndex].Item as Data.DataNodeDynamoType)?.TypeId ?? SelectedString;
+            }
+        }
+
+        /// <inheritdoc/>
+        [JsonIgnore]
+        public bool IsListValue => IsList;
+
         private bool isAutoMode = true; // default start with auto-detect 'on'
         private bool isList;
         private string displayValue = Properties.Resources.DefineDataDisplayValueMessage;
diff --git a/src/Libraries/CoreNodes/Data.cs b/src/Libraries/CoreNodes/Data.cs
index 959586acacc..d28f2e098ac 100644
--- a/src/Libraries/CoreNodes/Data.cs
+++ b/src/Libraries/CoreNodes/Data.cs
@@ -534,7 +534,7 @@ public static Dictionary<string, object> Remember([ArbitraryDimensionArrayImport
         /// <summary>
         /// A class representing a DataType supported by Dynamo
         /// </summary>
-        internal class DataNodeDynamoType(Type type, string name = null)
+        internal class DataNodeDynamoType(Type type, string name = null, string typeId = null)
         {
             /// <summary>
             /// The underlying Type
@@ -545,6 +545,17 @@ internal class DataNodeDynamoType(Type type, string name = null)
             /// </summary>
             public string Name { get; private set; } = name ?? type.Name;
             /// <summary>
+            /// Wire-format $typeid as emitted by ProtoGeometry's ToJson() / DSCore.Data.StringifyJSON
+            /// (e.g. "autodesk.math:point3d-1.0.0", "autodesk.geometry.curve:bcurve-1.0.0").
+            /// Null for primitive types (bool, string, Number, etc.) that don't use $typeid serialization.
+            /// Must match the identifiers recognised by <see cref="DynamoJObjectToNative"/>
+            /// and the actual $typeid values produced by ProtoGeometry serialization.
+            /// Exposed to external consumers via <see cref="Dynamo.Graph.Nodes.IValueSchemaProvider.ValueTypeId"/>
+            /// (implemented by DefineData), which DynamoPlayer reads to populate
+            /// ValueSchema.TypeId and DynamoMCP uses to resolve JSON Schemas for LLM inputs.
+            /// </summary>
+            public string TypeId { get; private set; } = typeId;
+            /// <summary>
             /// The hierarchical level to be displayed in the UI
             /// </summary>
             public int Level { get; private set; } = 0;
@@ -557,8 +568,8 @@ internal class DataNodeDynamoType(Type type, string name = null)
             /// </summary>
             public DataNodeDynamoType Parent { get; private set; }
 
-            public DataNodeDynamoType(Type type, int level, bool isLastChild = false, string name = null, DataNodeDynamoType parent = null)
-            : this(type, name)
+            public DataNodeDynamoType(Type type, int level, bool isLastChild = false, string name = null, DataNodeDynamoType parent = null, string typeId = null)
+            : this(type, name, typeId)
             {
                 Level = level;
                 IsLastChild = isLastChild;
@@ -577,41 +588,41 @@ public DataNodeDynamoType(Type type, int level, bool isLastChild = false, string
         /// </summary>
         static Data()
         {
-            var curve = new DataNodeDynamoType(typeof(Curve), 0, false, null, null);
-            var polyCurve = new DataNodeDynamoType(typeof(PolyCurve), 1, false, null, curve);
-            var polygon = new DataNodeDynamoType(typeof(Polygon), 2, false, null, polyCurve);  // polygon is subtype of polyCurve
-            var rectangle = new DataNodeDynamoType(typeof(Autodesk.DesignScript.Geometry.Rectangle), 3, true, null, polyCurve);    // rectangle is subtype of polygon
-            var solid = new DataNodeDynamoType(typeof(Solid), 0, false, null, null);
-            var cone = new DataNodeDynamoType(typeof(Cone), 1, false, null, solid);    // cone is subtype of solid
-            var cylinder = new DataNodeDynamoType(typeof(Cylinder), 2, false, null, cone); // cylinder is subtype of cone 
-            var cuboid = new DataNodeDynamoType(typeof(Cuboid), 1, false, null, solid);    // cuboid is subtype of solid
-            var sphere = new DataNodeDynamoType(typeof(Sphere), 1, true, null, solid);    // sphere is subtype of solid
-
-            var surface = new DataNodeDynamoType(typeof(Surface), 0, false, null, null);
+            var curve = new DataNodeDynamoType(typeof(Curve), 0, false, null, null, "dynamo.geometry:sab-1.0.0");
+            var polyCurve = new DataNodeDynamoType(typeof(PolyCurve), 1, false, null, curve, "autodesk.geometry.curve:compositecurve-1.0.0");
+            var polygon = new DataNodeDynamoType(typeof(Polygon), 2, false, null, polyCurve, "autodesk.geometry.curve:polyline-1.0.0");
+            var rectangle = new DataNodeDynamoType(typeof(Autodesk.DesignScript.Geometry.Rectangle), 3, true, null, polyCurve, "dynamo.geometry:rectangle-1.0.0");
+            var solid = new DataNodeDynamoType(typeof(Solid), 0, false, null, null, "dynamo.geometry:sab-1.0.0");
+            var cone = new DataNodeDynamoType(typeof(Cone), 1, false, null, solid, "dynamo.geometry:cone-1.0.0");
+            var cylinder = new DataNodeDynamoType(typeof(Cylinder), 2, false, null, cone, "autodesk.geometry.surface:cylinder-2.0.0");
+            var cuboid = new DataNodeDynamoType(typeof(Cuboid), 1, false, null, solid, "dynamo.geometry:cuboid-1.0.0");
+            var sphere = new DataNodeDynamoType(typeof(Sphere), 1, true, null, solid, "autodesk.geometry.surface:sphere-1.0.0");
+
+            var surface = new DataNodeDynamoType(typeof(Surface), 0, false, null, null, "dynamo.geometry:sab-1.0.0");
 
             var typeList = new List<DataNodeDynamoType>
             {
                 new(typeof(bool)),
-                new(typeof(BoundingBox)),
-                new(typeof(CoordinateSystem)),
+                new(typeof(BoundingBox), typeId: "autodesk.geometry:boundingbox3d-1.0.0"),
+                new(typeof(CoordinateSystem), typeId: "autodesk.math:matrix44d-1.0.0"),
                 curve,
-                new(typeof(Arc), 1, false, null, curve),
-                new(typeof(Circle), 1, false, null, curve),
-                new(typeof(Ellipse), 1, false, null, curve),
-                new(typeof(EllipseArc), 1, false, null, curve),
-                new(typeof(Helix), 1, false, null, curve),
-                new(typeof(Line), 1, false, null, curve),
-                new(typeof(NurbsCurve), 1, false, null, curve),
+                new(typeof(Arc), 1, false, null, curve, "autodesk.geometry.curve:circle-1.0.0"),
+                new(typeof(Circle), 1, false, null, curve, "autodesk.geometry.curve:circle-1.0.0"),
+                new(typeof(Ellipse), 1, false, null, curve, "autodesk.geometry.curve:ellipse-1.0.0"),
+                new(typeof(EllipseArc), 1, false, null, curve, "autodesk.geometry.curve:ellipse-1.0.0"),
+                new(typeof(Helix), 1, false, null, curve, "dynamo.geometry:sab-1.0.0"),
+                new(typeof(Line), 1, false, null, curve, "autodesk.geometry.curve:line-1.0.0"),
+                new(typeof(NurbsCurve), 1, false, null, curve, "autodesk.geometry.curve:bcurve-1.0.0"),
                 polyCurve,
                 polygon,
                 rectangle,
                 new(typeof(System.DateTime)),
                 new(typeof(double), "Number"),
                 new(typeof(long), "Integer"),
-                new(typeof(Location)),
-                new(typeof(Mesh)),
-                new(typeof(Plane)),
-                new(typeof(Autodesk.DesignScript.Geometry.Point)),
+                new(typeof(Location), typeId: "dynamo.data:location-1.0.0"),
+                new(typeof(Mesh), typeId: "dynamo.geometry:mesh-1.0.0"),
+                new(typeof(Plane), typeId: "autodesk.geometry.surface:plane-1.0.0"),
+                new(typeof(Autodesk.DesignScript.Geometry.Point), typeId: "autodesk.math:point3d-1.0.0"),
                 solid,
                 cone,
                 cylinder,
@@ -619,11 +630,11 @@ static Data()
                 sphere,
                 new(typeof(string)),
                 surface,
-                new(typeof(NurbsSurface), 1, false, null, surface),
-                new(typeof(PolySurface), 1, true, null, surface),
+                new(typeof(NurbsSurface), 1, false, null, surface, "autodesk.geometry.curve:bsurface-1.0.0"),
+                new(typeof(PolySurface), 1, true, null, surface, "dynamo.geometry:sab-1.0.0"),
                 new(typeof(System.TimeSpan)),
-                new(typeof(UV)),
-                new(typeof(Vector))
+                new(typeof(UV), typeId: "autodesk.math:uv-1.0.0"),
+                new(typeof(Vector), typeId: "autodesk.math:vector3d-1.0.0")
             };
 
             DataNodeDynamoTypeList = new ReadOnlyCollection<DataNodeDynamoType>(typeList);
diff --git a/test/DynamoCoreTests/Nodes/DefineDataTests.cs b/test/DynamoCoreTests/Nodes/DefineDataTests.cs
new file mode 100644
index 00000000000..982930d3913
--- /dev/null
+++ b/test/DynamoCoreTests/Nodes/DefineDataTests.cs
@@ -0,0 +1,59 @@
+using System.Collections.Generic;
+using System.Linq;
+using CoreNodeModels;
+using NUnit.Framework;
+
+namespace Dynamo.Tests.Nodes
+{
+    [TestFixture]
+    internal class DefineDataTests : DynamoModelTestBase
+    {
+        protected override void GetLibrariesToPreload(List<string> libraries)
+        {
+            libraries.Add("DSCoreNodes.dll");
+            base.GetLibrariesToPreload(libraries);
+        }
+
+        [Test]
+        [Category("UnitTests")]
+        public void ValueSchemaProviderReturnsTypeId()
+        {
+            var node = new DefineData();
+            CurrentDynamoModel.CurrentWorkspace.AddAndRegisterNode(node, false);
+
+            // Find a type with a non-null TypeId for testing
+            var pointType = DSCore.Data.DataNodeDynamoTypeList.First(t => t.Type == typeof(Autodesk.DesignScript.Geometry.Point));
+            Assert.IsNotNull(pointType.TypeId, "Point type should have a valid TypeId");
+            
+            // Set the node to Point type
+            node.SelectedIndex = DSCore.Data.DataNodeDynamoTypeList.IndexOf(pointType);
+            
+            Assert.AreEqual(pointType.TypeId, node.ValueTypeId);
+            Assert.IsFalse(node.IsListValue);
+        }
+
+        [Test]
+        [Category("UnitTests")]
+        public void ValueTypeIdSafeWhenNoSelection()
+        {
+            var node = new DefineData();
+            Assert.DoesNotThrow(() => { var _ = node.ValueTypeId; });
+            Assert.AreEqual(node.SelectedString, node.ValueTypeId);
+        }
+
+        [Test]
+        [Category("UnitTests")]
+        public void ValueTypeIdHandlesNullTypeId()
+        {
+            var node = new DefineData();
+            CurrentDynamoModel.CurrentWorkspace.AddAndRegisterNode(node, false);
+
+            // Default selection (bool) has null TypeId
+            var firstType = DSCore.Data.DataNodeDynamoTypeList.First();
+            Assert.IsNull(firstType.TypeId, "First type (bool) should have null TypeId");
+            
+            // Should fall back to SelectedString when TypeId is null
+            Assert.AreEqual(node.SelectedString, node.ValueTypeId);
+        }
+    }
+}