diff --git a/src/ZB.MOM.WW.ScadaBridge.Commons/Types/DataConnections/OpcUaReferenceForm.cs b/src/ZB.MOM.WW.ScadaBridge.Commons/Types/DataConnections/OpcUaReferenceForm.cs
new file mode 100644
index 00000000..b4c963d5
--- /dev/null
+++ b/src/ZB.MOM.WW.ScadaBridge.Commons/Types/DataConnections/OpcUaReferenceForm.cs
@@ -0,0 +1,55 @@
+using System.Globalization;
+
+namespace ZB.MOM.WW.ScadaBridge.Commons.Types.DataConnections;
+
+/// <summary>
+/// Pure, protocol-package-free classification of an OPC UA node-reference string's
+/// <i>form</i> — used by authoring UI to nudge operators toward index-durable bindings.
+/// </summary>
+/// <remarks>
+/// A bare <c>ns=&lt;index&gt;;…</c> reference hard-codes a namespace <i>index</i>, which is
+/// only meaningful relative to one server's namespace table. The OtOpcUa v3.0 raw/uns
+/// split makes this actively dangerous: v2's sole custom namespace and v3's <c>raw</c>
+/// tree both land at <c>ns=2</c>, so a stored <c>ns=2;s=…</c> resolves without error but
+/// silently now means a raw-tree node. The durable form is <c>nsu=&lt;uri&gt;;…</c>,
+/// resolved against the live namespace table at use time by
+/// <c>OpcUaNodeReference.Resolve</c>. This helper only classifies the string; it does not
+/// parse or resolve NodeIds (that stays in the DataConnectionLayer seam, which owns the
+/// <c>Opc.Ua</c> dependency).
+/// </remarks>
+public static class OpcUaReferenceForm
+{
+    /// <summary>
+    /// True when <paramref name="reference"/> is index-durable — the durable
+    /// <c>nsu=&lt;uri&gt;;…</c> form, spec-fixed <c>ns=0</c>, a short form with no namespace
+    /// prefix, or empty/whitespace (nothing to warn about). False only for a bare
+    /// server-namespace index (<c>ns=&lt;n&gt;;…</c> with n ≥ 1).
+    /// </summary>
+    public static bool IsDurable(string? reference)
+    {
+        if (string.IsNullOrWhiteSpace(reference))
+            return true;
+
+        var trimmed = reference.Trim();
+
+        // nsu=<uri>;… is the durable form (and its "ns" prefix must be checked before the
+        // bare "ns=" branch below, since "nsu=" also starts with "ns").
+        if (trimmed.StartsWith("nsu=", StringComparison.OrdinalIgnoreCase))
+            return true;
+
+        // Not a bare namespace-index reference at all → short forms (i=85, s=Foo) that
+        // imply namespace 0, which is spec-fixed and already durable.
+        if (!trimmed.StartsWith("ns=", StringComparison.OrdinalIgnoreCase))
+            return true;
+
+        // ns=<digits>;…  — parse the index; ns=0 is spec-fixed (durable), n ≥ 1 is bare.
+        var semicolon = trimmed.IndexOf(';');
+        var digits = semicolon >= 0 ? trimmed[3..semicolon] : trimmed[3..];
+        if (int.TryParse(digits, NumberStyles.None, CultureInfo.InvariantCulture, out var index))
+            return index == 0;
+
+        // Malformed "ns=" with non-numeric index — not a recognisable bare index; leave
+        // the real parse/reject to OpcUaNodeReference.Resolve. Don't warn on it here.
+        return true;
+    }
+}
diff --git a/tests/ZB.MOM.WW.ScadaBridge.Commons.Tests/Types/DataConnections/OpcUaReferenceFormTests.cs b/tests/ZB.MOM.WW.ScadaBridge.Commons.Tests/Types/DataConnections/OpcUaReferenceFormTests.cs
new file mode 100644
index 00000000..63fb12f7
--- /dev/null
+++ b/tests/ZB.MOM.WW.ScadaBridge.Commons.Tests/Types/DataConnections/OpcUaReferenceFormTests.cs
@@ -0,0 +1,27 @@
+using ZB.MOM.WW.ScadaBridge.Commons.Types.DataConnections;
+
+namespace ZB.MOM.WW.ScadaBridge.Commons.Tests.Types.DataConnections;
+
+public class OpcUaReferenceFormTests
+{
+    [Theory]
+    // durable → true
+    [InlineData("nsu=https://zb.com/otopcua/raw;s=Line1.Pump.Speed", true)]
+    [InlineData("nsu=https://zb.com/otopcua/uns;s=AreaA/Line1/Pump/Speed", true)]
+    [InlineData("NSU=https://x;s=y", true)]           // case-insensitive prefix
+    [InlineData("ns=0;i=85", true)]                    // spec-fixed namespace 0
+    [InlineData("i=85", true)]                         // short form, implicit ns0
+    [InlineData("s=Devices.Pump1", true)]              // no namespace prefix
+    [InlineData("", true)]                             // nothing typed
+    [InlineData("   ", true)]
+    [InlineData(null, true)]
+    // bare server-namespace index → false (warn)
+    [InlineData("ns=2;s=MyDevice.Temperature", false)]
+    [InlineData("ns=1;i=1001", false)]
+    [InlineData("ns=10;s=x", false)]
+    [InlineData("  ns=3;s=x  ", false)]                // trimmed before inspection
+    public void IsDurable_classifies_reference_forms(string? reference, bool expected)
+    {
+        Assert.Equal(expected, OpcUaReferenceForm.IsDurable(reference));
+    }
+}