diff --git a/core/Azure.Mcp.Core/tests/Azure.Mcp.Core.Tests/Areas/Server/Commands/ToolLoading/NamespaceToolLoaderTests.cs b/core/Azure.Mcp.Core/tests/Azure.Mcp.Core.Tests/Areas/Server/Commands/ToolLoading/NamespaceToolLoaderTests.cs
index 7740464cb1..f09f4d3491 100644
--- a/core/Azure.Mcp.Core/tests/Azure.Mcp.Core.Tests/Areas/Server/Commands/ToolLoading/NamespaceToolLoaderTests.cs
+++ b/core/Azure.Mcp.Core/tests/Azure.Mcp.Core.Tests/Areas/Server/Commands/ToolLoading/NamespaceToolLoaderTests.cs
@@ -958,4 +958,115 @@ public async ValueTask DisposeAsync()
 
         GC.SuppressFinalize(this);
     }
+
+    [Fact]
+    public void TryEmitSubscriptionTag_AddsTag_WhenSubscriptionParameterIsString()
+    {
+        // Arrange
+        const string expectedSubscription = "11111111-1111-1111-1111-111111111111";
+        var parameters = new Dictionary<string, JsonElement>(StringComparer.OrdinalIgnoreCase)
+        {
+            ["subscription"] = JsonSerializer.SerializeToElement(expectedSubscription),
+            ["vault"] = JsonSerializer.SerializeToElement("myvault"),
+        };
+
+        using var activity = new System.Diagnostics.Activity("test-activity");
+        activity.Start();
+
+        // Act
+        NamespaceToolLoader.TryEmitSubscriptionTag(parameters, activity);
+
+        // Assert
+        var tag = activity.GetTagItem(Microsoft.Mcp.Core.Services.Telemetry.AzureTagName.SubscriptionGuid);
+        Assert.Equal(expectedSubscription, tag);
+    }
+
+    [Fact]
+    public void TryEmitSubscriptionTag_MatchesKeyCaseInsensitively()
+    {
+        // Arrange
+        const string expectedSubscription = "22222222-2222-2222-2222-222222222222";
+        var parameters = new Dictionary<string, JsonElement>(StringComparer.Ordinal)
+        {
+            ["Subscription"] = JsonSerializer.SerializeToElement(expectedSubscription),
+        };
+
+        using var activity = new System.Diagnostics.Activity("test-activity");
+        activity.Start();
+
+        // Act
+        NamespaceToolLoader.TryEmitSubscriptionTag(parameters, activity);
+
+        // Assert
+        var tag = activity.GetTagItem(Microsoft.Mcp.Core.Services.Telemetry.AzureTagName.SubscriptionGuid);
+        Assert.Equal(expectedSubscription, tag);
+    }
+
+    [Fact]
+    public void TryEmitSubscriptionTag_DoesNothing_WhenNoSubscriptionParameter()
+    {
+        // Arrange
+        var parameters = new Dictionary<string, JsonElement>
+        {
+            ["vault"] = JsonSerializer.SerializeToElement("myvault"),
+        };
+
+        using var activity = new System.Diagnostics.Activity("test-activity");
+        activity.Start();
+
+        // Act
+        NamespaceToolLoader.TryEmitSubscriptionTag(parameters, activity);
+
+        // Assert
+        Assert.Null(activity.GetTagItem(Microsoft.Mcp.Core.Services.Telemetry.AzureTagName.SubscriptionGuid));
+    }
+
+    [Fact]
+    public void TryEmitSubscriptionTag_EmitsEmptyString_MatchingMcpRuntimeBehavior()
+    {
+        // Arrange
+        // McpRuntime.CallToolHandler emits the AzSubscriptionGuid tag for any non-null string,
+        // including empty. This test guards against drift between the two emission sites.
+        var parameters = new Dictionary<string, JsonElement>
+        {
+            ["subscription"] = JsonSerializer.SerializeToElement(string.Empty),
+        };
+
+        using var activity = new System.Diagnostics.Activity("test-activity");
+        activity.Start();
+
+        // Act
+        NamespaceToolLoader.TryEmitSubscriptionTag(parameters, activity);
+
+        // Assert
+        var tag = activity.GetTagItem(Microsoft.Mcp.Core.Services.Telemetry.AzureTagName.SubscriptionGuid);
+        Assert.Equal(string.Empty, tag);
+    }
+
+    [Fact]
+    public void TryEmitSubscriptionTag_DoesNothing_WhenActivityIsNull()
+    {
+        // Arrange
+        var parameters = new Dictionary<string, JsonElement>
+        {
+            ["subscription"] = JsonSerializer.SerializeToElement("abc"),
+        };
+
+        // Act & Assert (must not throw)
+        NamespaceToolLoader.TryEmitSubscriptionTag(parameters, activity: null);
+    }
+
+    [Fact]
+    public void TryEmitSubscriptionTag_DoesNothing_WhenParametersAreNull()
+    {
+        // Arrange
+        using var activity = new System.Diagnostics.Activity("test-activity");
+        activity.Start();
+
+        // Act
+        NamespaceToolLoader.TryEmitSubscriptionTag(parameters: null, activity);
+
+        // Assert
+        Assert.Null(activity.GetTagItem(Microsoft.Mcp.Core.Services.Telemetry.AzureTagName.SubscriptionGuid));
+    }
 }
diff --git a/core/Microsoft.Mcp.Core/src/Areas/Server/Commands/ToolLoading/NamespaceToolLoader.cs b/core/Microsoft.Mcp.Core/src/Areas/Server/Commands/ToolLoading/NamespaceToolLoader.cs
index 3a1d8c3452..d27cf39f76 100644
--- a/core/Microsoft.Mcp.Core/src/Areas/Server/Commands/ToolLoading/NamespaceToolLoader.cs
+++ b/core/Microsoft.Mcp.Core/src/Areas/Server/Commands/ToolLoading/NamespaceToolLoader.cs
@@ -13,6 +13,8 @@
 using Microsoft.Mcp.Core.Helpers;
 using Microsoft.Mcp.Core.Models;
 using Microsoft.Mcp.Core.Models.Command;
+using Microsoft.Mcp.Core.Models.Option;
+using Microsoft.Mcp.Core.Services.Telemetry;
 using ModelContextProtocol;
 using ModelContextProtocol.Protocol;
 
@@ -439,6 +441,11 @@ private async Task<CallToolResult> InvokeChildToolAsync(
                 .SetTag(TagName.ToolId, cmd.Id)
                 .SetTag(TagName.IsServerCommandInvoked, true);
 
+            // In namespace mode the McpRuntime sees only the outer {intent, command, parameters}
+            // envelope, so it cannot emit AzSubscriptionGuid from the top-level arguments. Emit it
+            // here from the inner parameter dictionary so per-subscription telemetry is captured.
+            TryEmitSubscriptionTag(parameters, currentActivity);
+
             var commandResponse = await cmd.ExecuteAsync(commandContext, commandOptions, cancellationToken);
             var jsonResponse = JsonSerializer.Serialize(commandResponse, ModelsJsonContext.Default.CommandResponse);
             var isError = commandResponse.Status < HttpStatusCode.OK || commandResponse.Status >= HttpStatusCode.Ambiguous;
@@ -672,6 +679,39 @@ private static bool IsRawMcpToolInputOption(Option option)
             string.Equals(NameNormalization.NormalizeOptionName(alias), RawMcpToolInputOptionName, StringComparison.OrdinalIgnoreCase));
     }
 
+    internal static void TryEmitSubscriptionTag(IDictionary<string, JsonElement>? parameters, Activity? activity)
+    {
+        if (activity == null || parameters == null || parameters.Count == 0)
+        {
+            return;
+        }
+
+        var normalizedSubscriptionName = NameNormalization.NormalizeOptionName(OptionDefinitions.Common.Subscription.Name);
+        foreach (var kvp in parameters)
+        {
+            if (!string.Equals(kvp.Key, normalizedSubscriptionName, StringComparison.OrdinalIgnoreCase))
+            {
+                continue;
+            }
+
+            if (kvp.Value.ValueKind != JsonValueKind.String)
+            {
+                return;
+            }
+
+            // Match McpRuntime.CallToolHandler: emit the tag for any non-null string,
+            // including empty values, so telemetry is consistent between direct-tool and
+            // namespace-mode invocations.
+            var subscription = kvp.Value.GetString();
+            if (subscription != null)
+            {
+                activity.AddTag(AzureTagName.SubscriptionGuid, subscription);
+            }
+
+            return;
+        }
+    }
+
     internal static Dictionary<string, JsonElement> GetParametersFromArgs(IDictionary<string, JsonElement>? args)
     {
         if (args == null)