Read default subscription from Azure CLI profile for all subscription-scoped commands

core/Azure.Mcp.Core/src/Areas/Subscription/Commands/SubscriptionJsonContext.cs

@@ -2,10 +2,12 @@
 // Licensed under the MIT License.
 
 using System.Text.Json.Serialization;
+using Azure.Mcp.Core.Areas.Subscription.Models;
 
 namespace Azure.Mcp.Core.Areas.Subscription.Commands;
 
 [JsonSerializable(typeof(SubscriptionListCommand.SubscriptionListCommandResult))]
+[JsonSerializable(typeof(SubscriptionInfo))]
 [JsonSourceGenerationOptions(PropertyNamingPolicy = JsonKnownNamingPolicy.CamelCase)]
 internal partial class SubscriptionJsonContext : JsonSerializerContext
 {

core/Azure.Mcp.Core/src/Areas/Subscription/Commands/SubscriptionListCommand.cs

@@ -1,6 +1,7 @@
 // Copyright (c) Microsoft Corporation.
 // Licensed under the MIT License.
 
+using Azure.Mcp.Core.Areas.Subscription.Models;
 using Azure.Mcp.Core.Areas.Subscription.Options;
 using Azure.Mcp.Core.Commands;
 using Azure.Mcp.Core.Services.Azure.Subscription;
@@ -21,7 +22,11 @@ public sealed class SubscriptionListCommand(ILogger<SubscriptionListCommand> log
     public override string Name => "list";
 
     public override string Description =>
-    "List all or current subscriptions for an account in Azure; returns subscriptionId, displayName, state, tenantId, and isDefault. Use for scope selection in governance, policy, access, cost management, or deployment.";
+        "List all Azure subscriptions for the current account. Returns subscriptionId, displayName, state, tenantId, and isDefault for each subscription. " +
+        "The isDefault field indicates the user's default subscription as configured via 'az account set' in the Azure CLI profile. " +
+        "When the user has not specified a subscription, prefer the subscription where isDefault is true. " +
+        "If no default is set and multiple subscriptions exist, ask the user which subscription to use.";
+
     public override string Title => CommandTitle;
 
     public override ToolMetadata Metadata => new()
@@ -48,8 +53,11 @@ public override async Task<CommandResponse> ExecuteAsync(CommandContext context,
             var subscriptionService = context.GetService<ISubscriptionService>();
             var subscriptions = await subscriptionService.GetSubscriptions(options.Tenant, options.RetryPolicy, cancellationToken);
 
+            var defaultSubscriptionId = subscriptionService.GetDefaultSubscriptionId();
+            var subscriptionInfos = MapToSubscriptionInfos(subscriptions, defaultSubscriptionId);
+
             context.Response.Results = ResponseResult.Create(
-                    new SubscriptionListCommandResult(subscriptions),
+                    new SubscriptionListCommandResult(subscriptionInfos),
                     SubscriptionJsonContext.Default.SubscriptionListCommandResult);
         }
         catch (Exception ex)
@@ -61,5 +69,26 @@ public override async Task<CommandResponse> ExecuteAsync(CommandContext context,
         return context.Response;
     }
 
-    internal record SubscriptionListCommandResult(List<SubscriptionData> Subscriptions);
+    internal static List<SubscriptionInfo> MapToSubscriptionInfos(List<SubscriptionData> subscriptions, string? defaultSubscriptionId)
+    {
+        var hasDefault = !string.IsNullOrEmpty(defaultSubscriptionId);
+
+        var infos = subscriptions.Select(s => new SubscriptionInfo(
+            s.SubscriptionId,
+            s.DisplayName,
+            s.State?.ToString(),
+            s.TenantId?.ToString(),
+            hasDefault && s.SubscriptionId.Equals(defaultSubscriptionId, StringComparison.OrdinalIgnoreCase)
+        )).ToList();
+
+        // Sort so the default subscription appears first
+        if (hasDefault)
+        {
+            infos = [.. infos.OrderByDescending(s => s.IsDefault)];
+        }
+
+        return infos;
+    }
+
+    internal record SubscriptionListCommandResult(List<SubscriptionInfo> Subscriptions);
 }

core/Azure.Mcp.Core/src/Areas/Subscription/Models/SubscriptionInfo.cs

@@ -0,0 +1,19 @@
+// Copyright (c) Microsoft Corporation.
+// Licensed under the MIT License.
+
+namespace Azure.Mcp.Core.Areas.Subscription.Models;
+
+/// <summary>
+/// Represents an Azure subscription with default subscription indicator.
+/// </summary>
+/// <param name="SubscriptionId">The subscription ID.</param>
+/// <param name="DisplayName">The display name of the subscription.</param>
+/// <param name="State">The subscription state (e.g., Enabled, Disabled).</param>
+/// <param name="TenantId">The tenant ID associated with the subscription.</param>
+/// <param name="IsDefault">Whether this subscription is the default as configured via 'az account set' in the Azure CLI profile, or via the AZURE_SUBSCRIPTION_ID environment variable.</param>
+internal record SubscriptionInfo(
+    string SubscriptionId,
+    string DisplayName,
+    string? State,
+    string? TenantId,
+    bool IsDefault);

core/Azure.Mcp.Core/src/Commands/Subscription/SubscriptionCommand.cs

@@ -18,8 +18,8 @@ protected override void RegisterOptions(Command command)
         command.Options.Add(OptionDefinitions.Common.Subscription);
         command.Validators.Add(commandResult =>
         {
-            // Command-level validation for presence: allow either --subscription or AZURE_SUBSCRIPTION_ID
-            // This mirrors the prior behavior that preferred the explicit option but fell back to env var.
+            // Command-level validation for presence: allow either --subscription,
+            // Azure CLI profile default, or AZURE_SUBSCRIPTION_ID env var.
             if (!CommandHelper.HasSubscriptionAvailable(commandResult))
             {
                 commandResult.AddError("Missing Required options: --subscription");

core/Azure.Mcp.Core/src/Services/Azure/Subscription/ISubscriptionService.cs

@@ -13,4 +13,11 @@ public interface ISubscriptionService
     bool IsSubscriptionId(string subscription, string? tenant = null);
     Task<string> GetSubscriptionIdByName(string subscriptionName, string? tenant = null, RetryPolicyOptions? retryPolicy = null, CancellationToken cancellationToken = default);
     Task<string> GetSubscriptionNameById(string subscriptionId, string? tenant = null, RetryPolicyOptions? retryPolicy = null, CancellationToken cancellationToken = default);
+
+    /// <summary>
+    /// Gets the default subscription ID from the Azure CLI profile (~/.azure/azureProfile.json).
+    /// Falls back to the AZURE_SUBSCRIPTION_ID environment variable if the profile is unavailable.
+    /// </summary>
+    /// <returns>The default subscription ID if found, null otherwise.</returns>
+    string? GetDefaultSubscriptionId();
 }

core/Azure.Mcp.Core/src/Services/Azure/Subscription/SubscriptionService.cs

@@ -1,6 +1,7 @@
 // Copyright (c) Microsoft Corporation.
 // Licensed under the MIT License.
 
+using Azure.Mcp.Core.Helpers;
 using Azure.Mcp.Core.Options;
 using Azure.Mcp.Core.Services.Azure.Tenant;
 using Azure.Mcp.Core.Services.Caching;
@@ -96,6 +97,12 @@ public async Task<string> GetSubscriptionNameById(string subscriptionId, string?
         return subscription.DisplayName;
     }
 
+    /// <inheritdoc/>
+    public string? GetDefaultSubscriptionId()
+    {
+        return CommandHelper.GetDefaultSubscription();
+    }
+
     private async Task<string> GetSubscriptionId(string subscription, string? tenant, RetryPolicyOptions? retryPolicy, CancellationToken cancellationToken)
     {
         if (IsSubscriptionId(subscription))

core/Azure.Mcp.Core/tests/Azure.Mcp.Core.UnitTests/Areas/Subscription/AzureCliProfileHelperTests.cs

@@ -0,0 +1,124 @@
+// Copyright (c) Microsoft Corporation.
+// Licensed under the MIT License.
+
+using Azure.Mcp.Core.Helpers;
+using Xunit;
+
+namespace Azure.Mcp.Core.UnitTests.Areas.Subscription;
+
+public class AzureCliProfileHelperTests
+{
+    [Fact]
+    public void ParseDefaultSubscriptionId_ValidProfile_ReturnsDefaultId()
+    {
+        var profileJson = """
+        {
+            "subscriptions": [
+                {
+                    "id": "sub-1111-1111",
+                    "name": "Subscription One",
+                    "state": "Enabled",
+                    "tenantId": "tenant-1111",
+                    "isDefault": false
+                },
+                {
+                    "id": "sub-2222-2222",
+                    "name": "Subscription Two",
+                    "state": "Enabled",
+                    "tenantId": "tenant-2222",
+                    "isDefault": true
+                },
+                {
+                    "id": "sub-3333-3333",
+                    "name": "Subscription Three",
+                    "state": "Enabled",
+                    "tenantId": "tenant-3333",
+                    "isDefault": false
+                }
+            ]
+        }
+        """;
+
+        var result = AzureCliProfileHelper.ParseDefaultSubscriptionId(profileJson);
+
+        Assert.Equal("sub-2222-2222", result);
+    }
+
+    [Fact]
+    public void ParseDefaultSubscriptionId_NoDefaultInProfile_ReturnsNull()
+    {
+        var profileJson = """
+        {
+            "subscriptions": [
+                {
+                    "id": "sub-1111-1111",
+                    "name": "Subscription One",
+                    "state": "Enabled",
+                    "tenantId": "tenant-1111",
+                    "isDefault": false
+                }
+            ]
+        }
+        """;
+
+        var result = AzureCliProfileHelper.ParseDefaultSubscriptionId(profileJson);
+
+        Assert.Null(result);
+    }
+
+    [Fact]
+    public void ParseDefaultSubscriptionId_EmptySubscriptions_ReturnsNull()
+    {
+        var profileJson = """
+        {
+            "subscriptions": []
+        }
+        """;
+
+        var result = AzureCliProfileHelper.ParseDefaultSubscriptionId(profileJson);
+
+        Assert.Null(result);
+    }
+
+    [Fact]
+    public void ParseDefaultSubscriptionId_NoSubscriptionsProperty_ReturnsNull()
+    {
+        var profileJson = """
+        {
+            "installationId": "some-id"
+        }
+        """;
+
+        var result = AzureCliProfileHelper.ParseDefaultSubscriptionId(profileJson);
+
+        Assert.Null(result);
+    }
+
+    [Fact]
+    public void ParseDefaultSubscriptionId_MissingIdOnDefault_ReturnsNull()
+    {
+        var profileJson = """
+        {
+            "subscriptions": [
+                {
+                    "name": "Subscription One",
+                    "isDefault": true
+                }
+            ]
+        }
+        """;
+
+        var result = AzureCliProfileHelper.ParseDefaultSubscriptionId(profileJson);
+
+        Assert.Null(result);
+    }
+
+    [Fact]
+    public void GetAzureProfilePath_ReturnsExpectedPath()
+    {
+        var result = AzureCliProfileHelper.GetAzureProfilePath();
+
+        Assert.Contains(".azure", result);
+        Assert.EndsWith("azureProfile.json", result);
+    }
+}