diff --git a/src/ZB.MOM.WW.MxGateway.Server/Sessions/ArrayAddressNormalizer.cs b/src/ZB.MOM.WW.MxGateway.Server/Sessions/ArrayAddressNormalizer.cs
new file mode 100644
index 0000000..9dfc0cd
--- /dev/null
+++ b/src/ZB.MOM.WW.MxGateway.Server/Sessions/ArrayAddressNormalizer.cs
@@ -0,0 +1,43 @@
+using ZB.MOM.WW.MxGateway.Server.Galaxy;
+
+namespace ZB.MOM.WW.MxGateway.Server.Sessions;
+
+/// <summary>
+///     Rewrites a bare MXAccess attribute address to its writable array form by appending the
+///     trailing <c>[]</c> suffix when Galaxy Repository metadata reports the attribute as an array.
+///     MXAccess requires the <c>[]</c> suffix on the AddItem address for an array attribute to be
+///     writable; the bare name registers a read-only-ish handle. This is best-effort: when metadata
+///     is cold, the address is unknown, or the attribute is not an array, the address is returned
+///     unchanged and no exception is thrown.
+/// </summary>
+public sealed class ArrayAddressNormalizer(IGalaxyHierarchyCache cache)
+{
+    private const string ArraySuffix = "[]";
+
+    /// <summary>
+    ///     Returns <paramref name="address"/> with a trailing <c>[]</c> appended when Galaxy metadata
+    ///     reports it as an array attribute; otherwise returns it unchanged. Never throws.
+    /// </summary>
+    /// <param name="address">The MXAccess attribute address to normalize.</param>
+    /// <returns>The normalized address, or the original address when no rewrite applies.</returns>
+    public string Normalize(string address)
+    {
+        if (string.IsNullOrWhiteSpace(address))
+        {
+            return address;
+        }
+
+        if (address.EndsWith(ArraySuffix, StringComparison.Ordinal))
+        {
+            return address;
+        }
+
+        // Galaxy SQL keys array attributes by their suffixed FullTagReference (e.g. "Obj.Arr[]"),
+        // so probe for the suffixed form to decide whether the bare name is an array.
+        string suffixed = address + ArraySuffix;
+        return cache.Current.Index.TagsByAddress.TryGetValue(suffixed, out GalaxyTagLookup? lookup)
+            && lookup.Attribute?.IsArray == true
+                ? suffixed
+                : address;
+    }
+}
diff --git a/src/ZB.MOM.WW.MxGateway.Tests/Gateway/Sessions/ArrayAddressNormalizerTests.cs b/src/ZB.MOM.WW.MxGateway.Tests/Gateway/Sessions/ArrayAddressNormalizerTests.cs
new file mode 100644
index 0000000..ad34fcb
--- /dev/null
+++ b/src/ZB.MOM.WW.MxGateway.Tests/Gateway/Sessions/ArrayAddressNormalizerTests.cs
@@ -0,0 +1,105 @@
+using ZB.MOM.WW.MxGateway.Contracts.Proto.Galaxy;
+using ZB.MOM.WW.MxGateway.Server.Galaxy;
+using ZB.MOM.WW.MxGateway.Server.Sessions;
+
+namespace ZB.MOM.WW.MxGateway.Tests.Gateway.Sessions;
+
+public sealed class ArrayAddressNormalizerTests
+{
+    /// <summary>Verifies a bare array attribute name gains the trailing array suffix.</summary>
+    [Fact]
+    public void Normalize_BareArrayName_AppendsArraySuffix()
+    {
+        ArrayAddressNormalizer normalizer = CreateNormalizer();
+
+        Assert.Equal("Obj.Arr[]", normalizer.Normalize("Obj.Arr"));
+    }
+
+    /// <summary>Verifies an already-suffixed address is returned unchanged.</summary>
+    [Fact]
+    public void Normalize_AlreadySuffixed_ReturnsUnchanged()
+    {
+        ArrayAddressNormalizer normalizer = CreateNormalizer();
+
+        Assert.Equal("Obj.Arr[]", normalizer.Normalize("Obj.Arr[]"));
+    }
+
+    /// <summary>Verifies a scalar attribute is returned unchanged.</summary>
+    [Fact]
+    public void Normalize_ScalarAttribute_ReturnsUnchanged()
+    {
+        ArrayAddressNormalizer normalizer = CreateNormalizer();
+
+        Assert.Equal("Obj.Scalar", normalizer.Normalize("Obj.Scalar"));
+    }
+
+    /// <summary>Verifies an address absent from the cache is returned unchanged.</summary>
+    [Fact]
+    public void Normalize_UnknownAddress_ReturnsUnchanged()
+    {
+        ArrayAddressNormalizer normalizer = CreateNormalizer();
+
+        Assert.Equal("Obj.Unknown", normalizer.Normalize("Obj.Unknown"));
+    }
+
+    /// <summary>Verifies null, empty, and whitespace addresses are returned unchanged.</summary>
+    [Theory]
+    [InlineData("")]
+    [InlineData("   ")]
+    public void Normalize_BlankAddress_ReturnsUnchanged(string address)
+    {
+        ArrayAddressNormalizer normalizer = CreateNormalizer();
+
+        Assert.Equal(address, normalizer.Normalize(address));
+    }
+
+    private static ArrayAddressNormalizer CreateNormalizer()
+    {
+        IReadOnlyList<GalaxyObject> objects =
+        [
+            new GalaxyObject
+            {
+                GobjectId = 1,
+                TagName = "Obj",
+                ContainedName = "Obj",
+                Attributes =
+                {
+                    new GalaxyAttribute
+                    {
+                        AttributeName = "Arr",
+                        // Galaxy SQL already appends "[]" to array attribute references.
+                        FullTagReference = "Obj.Arr[]",
+                        IsArray = true,
+                    },
+                    new GalaxyAttribute
+                    {
+                        AttributeName = "Scalar",
+                        FullTagReference = "Obj.Scalar",
+                        IsArray = false,
+                    },
+                },
+            },
+        ];
+
+        GalaxyHierarchyCacheEntry entry = GalaxyHierarchyCacheEntry.Empty with
+        {
+            Status = GalaxyCacheStatus.Healthy,
+            Objects = objects,
+            Index = GalaxyHierarchyIndex.Build(objects),
+        };
+
+        return new ArrayAddressNormalizer(new StubGalaxyHierarchyCache(entry));
+    }
+
+    private sealed class StubGalaxyHierarchyCache(GalaxyHierarchyCacheEntry current) : IGalaxyHierarchyCache
+    {
+        /// <summary>Gets the current cache entry.</summary>
+        public GalaxyHierarchyCacheEntry Current { get; } = current;
+
+        /// <inheritdoc />
+        public Task RefreshAsync(CancellationToken cancellationToken) => Task.CompletedTask;
+
+        /// <inheritdoc />
+        public Task WaitForFirstLoadAsync(CancellationToken cancellationToken) => Task.CompletedTask;
+    }
+}