Implemented MCP Set Log Level

src/Azure.DataApiBuilder.Mcp/Core/McpStdioServer.cs

@@ -6,6 +6,7 @@
 using Azure.DataApiBuilder.Config.ObjectModel;
 using Azure.DataApiBuilder.Core.AuthenticationHelpers.AuthenticationSimulator;
 using Azure.DataApiBuilder.Core.Configurations;
+using Azure.DataApiBuilder.Core.Telemetry;
 using Azure.DataApiBuilder.Mcp.Model;
 using Azure.DataApiBuilder.Mcp.Utils;
 using Microsoft.AspNetCore.Http;
@@ -131,6 +132,10 @@ public async Task RunAsync(CancellationToken cancellationToken)
                                 WriteResult(id, new { ok = true });
                                 break;
 
+                            case "logging/setLevel":
+                                HandleSetLogLevel(id, root);
+                                break;
+
                             case "shutdown":
                                 WriteResult(id, new { ok = true });
                                 return;
@@ -228,6 +233,71 @@ private void HandleListTools(JsonElement? id)
             WriteResult(id, new { tools = toolsWire });
         }
 
+        /// <summary>
+        /// Handles the "logging/setLevel" JSON-RPC method by updating the runtime log level.
+        /// </summary>
+        /// <param name="id">The request identifier extracted from the incoming JSON-RPC request.</param>
+        /// <param name="root">The root JSON element of the incoming JSON-RPC request.</param>
+        /// <remarks>
+        /// Log level precedence (highest to lowest):
+        /// 1. CLI --LogLevel flag - cannot be overridden
+        /// 2. Config runtime.telemetry.log-level - cannot be overridden by MCP
+        /// 3. MCP logging/setLevel - only works if neither CLI nor Config explicitly set a level
+        /// 
+        /// If CLI or Config set the log level, this method accepts the request but silently ignores it.
+        /// The client won't get an error, but CLI/Config wins.
+        /// </remarks>
+        private void HandleSetLogLevel(JsonElement? id, JsonElement root)
+        {
+            // Extract the level parameter from the request
+            string? level = null;
+            if (root.TryGetProperty("params", out JsonElement paramsEl) &&
+                paramsEl.TryGetProperty("level", out JsonElement levelEl) &&
+                levelEl.ValueKind == JsonValueKind.String)
+            {
+                level = levelEl.GetString();
+            }
+
+            if (string.IsNullOrWhiteSpace(level))
+            {
+                WriteError(id, McpStdioJsonRpcErrorCodes.INVALID_PARAMS, "Missing or invalid 'level' parameter");
+                return;
+            }
+
+            // Get the ILogLevelController from service provider
+            ILogLevelController? logLevelController = _serviceProvider.GetService<ILogLevelController>();
+            if (logLevelController is null)
+            {
+                // Log level controller not available - still accept request per MCP spec
+                Console.Error.WriteLine("[MCP DEBUG] ILogLevelController not available, logging/setLevel ignored.");
+                WriteResult(id, new { });
+                return;
+            }
+
+            // Attempt to update the log level
+            // If CLI or Config overrode, this returns false but we still return success to the client
+            bool changed = logLevelController.UpdateFromMcp(level);
+            if (changed)
+            {
+                Console.Error.WriteLine($"[MCP DEBUG] Log level changed to: {level}");
+            }
+            else if (logLevelController.IsCliOverridden)
+            {
+                Console.Error.WriteLine($"[MCP DEBUG] Log level not changed (CLI override active), requested: {level}");
+            }
+            else if (logLevelController.IsConfigOverridden)
+            {
+                Console.Error.WriteLine($"[MCP DEBUG] Log level not changed (Config override active), requested: {level}");
+            }
+            else
+            {
+                Console.Error.WriteLine($"[MCP DEBUG] Log level not changed, invalid level: {level}");
+            }
+
+            // Always return success (empty result object) per MCP spec
+            WriteResult(id, new { });
+        }
+
         /// <summary>
         /// Handles the "tools/call" JSON-RPC method by executing the specified tool with the provided arguments.
         /// </summary>

src/Cli/ConfigGenerator.cs

@@ -2582,7 +2582,8 @@ public static bool TryStartEngineWithOptions(StartOptions options, FileSystemRun
             List<string> args = new()
             { "--ConfigFileName", runtimeConfigFile };
 
-            /// Add arguments for LogLevel. Checks if LogLevel is overridden with option `--LogLevel`.
+            /// Add arguments for LogLevel. Only pass --LogLevel when user explicitly specified it,
+            /// so that MCP logging/setLevel can still adjust the level when no CLI override is present.
             /// If not provided, Default minimum LogLevel is Debug for Development mode and Error for Production mode.
             LogLevel minimumLogLevel;
             if (options.LogLevel is not null)
@@ -2597,17 +2598,22 @@ public static bool TryStartEngineWithOptions(StartOptions options, FileSystemRun
 
                 minimumLogLevel = (LogLevel)options.LogLevel;
                 _logger.LogInformation("Setting minimum LogLevel: {minimumLogLevel}.", minimumLogLevel);
+
+                // Only add --LogLevel when user explicitly specified it via CLI.
+                // This allows MCP logging/setLevel to work when no CLI override is present.
+                args.Add("--LogLevel");
+                args.Add(minimumLogLevel.ToString());
             }
             else
             {
                 minimumLogLevel = deserializedRuntimeConfig.GetConfiguredLogLevel();
                 HostMode hostModeType = deserializedRuntimeConfig.IsDevelopmentMode() ? HostMode.Development : HostMode.Production;
 
                 _logger.LogInformation($"Setting default minimum LogLevel: {minimumLogLevel} for {hostModeType} mode.", minimumLogLevel, hostModeType);
-            }
 
-            args.Add("--LogLevel");
-            args.Add(minimumLogLevel.ToString());
+                // Don't add --LogLevel arg since user didn't explicitly set it.
+                // Service will determine default log level based on config or host mode.
+            }
 
             // This will add args to disable automatic redirects to https if specified by user
             if (options.IsHttpsRedirectionDisabled)

src/Core/Telemetry/ILogLevelController.cs

@@ -0,0 +1,37 @@
+// Copyright (c) Microsoft Corporation.
+// Licensed under the MIT License.
+
+namespace Azure.DataApiBuilder.Core.Telemetry
+{
+    /// <summary>
+    /// Interface for controlling log levels dynamically at runtime.
+    /// This allows MCP and other components to adjust logging without
+    /// direct coupling to the concrete implementation.
+    /// </summary>
+    public interface ILogLevelController
+    {
+        /// <summary>
+        /// Gets a value indicating whether the log level was overridden by CLI arguments.
+        /// When true, MCP and config-based log level changes are ignored.
+        /// </summary>
+        bool IsCliOverridden { get; }
+
+        /// <summary>
+        /// Gets a value indicating whether the log level was explicitly set in the config file.
+        /// When true along with IsCliOverridden being false, MCP log level changes are ignored.
+        /// </summary>
+        bool IsConfigOverridden { get; }
+
+        /// <summary>
+        /// Updates the log level from an MCP logging/setLevel request.
+        /// The MCP level string is mapped to the appropriate LogLevel.
+        /// Log level precedence (highest to lowest):
+        /// 1. CLI --LogLevel flag (IsCliOverridden = true)
+        /// 2. Config runtime.telemetry.log-level (IsConfigOverridden = true)
+        /// 3. MCP logging/setLevel (only works if neither CLI nor Config set a level)
+        /// </summary>
+        /// <param name="mcpLevel">The MCP log level string (e.g., "debug", "info", "warning", "error").</param>
+        /// <returns>True if the level was changed; false if CLI or Config override prevented the change.</returns>
+        bool UpdateFromMcp(string mcpLevel);
+    }
+}

src/Service.Tests/UnitTests/DynamicLogLevelProviderTests.cs

@@ -0,0 +1,92 @@
+// Copyright (c) Microsoft Corporation.
+// Licensed under the MIT License.
+
+#nullable enable
+
+using Azure.DataApiBuilder.Service.Telemetry;
+using Microsoft.Extensions.Logging;
+using Microsoft.VisualStudio.TestTools.UnitTesting;
+
+namespace Azure.DataApiBuilder.Service.Tests.UnitTests
+{
+    /// <summary>
+    /// Unit tests for the DynamicLogLevelProvider class.
+    /// Tests the MCP logging/setLevel support.
+    /// </summary>
+    [TestClass]
+    public class DynamicLogLevelProviderTests
+    {
+        [TestMethod]
+        public void UpdateFromMcp_ValidLevel_ChangesLogLevel()
+        {
+            // Arrange
+            DynamicLogLevelProvider provider = new();
+            provider.SetInitialLogLevel(LogLevel.Error, isCliOverridden: false);
+
+            // Act
+            bool result = provider.UpdateFromMcp("debug");
+
+            // Assert
+            Assert.IsTrue(result);
+            Assert.AreEqual(LogLevel.Debug, provider.CurrentLogLevel);
+        }
+
+        [TestMethod]
+        public void UpdateFromMcp_CliOverridden_DoesNotChangeLogLevel()
+        {
+            // Arrange
+            DynamicLogLevelProvider provider = new();
+            provider.SetInitialLogLevel(LogLevel.Error, isCliOverridden: true);
+
+            // Act
+            bool result = provider.UpdateFromMcp("debug");
+
+            // Assert
+            Assert.IsFalse(result);
+            Assert.AreEqual(LogLevel.Error, provider.CurrentLogLevel);
+        }
+
+        [TestMethod]
+        public void UpdateFromMcp_ConfigOverridden_DoesNotChangeLogLevel()
+        {
+            // Arrange
+            DynamicLogLevelProvider provider = new();
+            provider.SetInitialLogLevel(LogLevel.Warning, isCliOverridden: false, isConfigOverridden: true);
+
+            // Act
+            bool result = provider.UpdateFromMcp("debug");
+
+            // Assert
+            Assert.IsFalse(result);
+            Assert.AreEqual(LogLevel.Warning, provider.CurrentLogLevel);
+        }
+
+        [TestMethod]
+        public void UpdateFromMcp_InvalidLevel_ReturnsFalse()
+        {
+            // Arrange
+            DynamicLogLevelProvider provider = new();
+            provider.SetInitialLogLevel(LogLevel.Error, isCliOverridden: false);
+
+            // Act
+            bool result = provider.UpdateFromMcp("invalid");
+
+            // Assert
+            Assert.IsFalse(result);
+            Assert.AreEqual(LogLevel.Error, provider.CurrentLogLevel);
+        }
+
+        [TestMethod]
+        public void ShouldLog_ReturnsCorrectResult()
+        {
+            // Arrange
+            DynamicLogLevelProvider provider = new();
+            provider.SetInitialLogLevel(LogLevel.Warning, isCliOverridden: false);
+
+            // Assert - logs at or above Warning should pass
+            Assert.IsTrue(provider.ShouldLog(LogLevel.Warning));
+            Assert.IsTrue(provider.ShouldLog(LogLevel.Error));
+            Assert.IsFalse(provider.ShouldLog(LogLevel.Debug));
+        }
+    }
+}

src/Service/Program.cs

@@ -9,6 +9,7 @@
 using System.Text.RegularExpressions;
 using System.Threading.Tasks;
 using Azure.DataApiBuilder.Config;
+using Azure.DataApiBuilder.Core.Telemetry;
 using Azure.DataApiBuilder.Service.Exceptions;
 using Azure.DataApiBuilder.Service.Telemetry;
 using Azure.DataApiBuilder.Service.Utilities;
@@ -110,6 +111,7 @@ public static IHostBuilder CreateHostBuilder(string[] args, bool runMcpStdio, st
                 .ConfigureServices((context, services) =>
                 {
                     services.AddSingleton(LogLevelProvider);
+                    services.AddSingleton<ILogLevelController>(LogLevelProvider);
                 })
                 .ConfigureLogging(logging =>
                 {

src/Service/Telemetry/DynamicLogLevelProvider.cs

@@ -1,17 +1,43 @@
+using System;
+using System.Collections.Generic;
 using Azure.DataApiBuilder.Config.ObjectModel;
+using Azure.DataApiBuilder.Core.Telemetry;
 using Microsoft.Extensions.Logging;
 
 namespace Azure.DataApiBuilder.Service.Telemetry
 {
-    public class DynamicLogLevelProvider
+    /// <summary>
+    /// Provides dynamic log level control with support for CLI override, runtime config, and MCP.
+    /// </summary>
+    public class DynamicLogLevelProvider : ILogLevelController
     {
+        /// <summary>
+        /// Maps MCP log level strings to Microsoft.Extensions.Logging.LogLevel.
+        /// MCP levels: debug, info, notice, warning, error, critical, alert, emergency.
+        /// </summary>
+        private static readonly Dictionary<string, LogLevel> _mcpLevelMapping = new(StringComparer.OrdinalIgnoreCase)
+        {
+            ["debug"] = LogLevel.Debug,
+            ["info"] = LogLevel.Information,
+            ["notice"] = LogLevel.Information, // MCP "notice" maps to Information (no direct equivalent)
+            ["warning"] = LogLevel.Warning,
+            ["error"] = LogLevel.Error,
+            ["critical"] = LogLevel.Critical,
+            ["alert"] = LogLevel.Critical,     // MCP "alert" maps to Critical
+            ["emergency"] = LogLevel.Critical  // MCP "emergency" maps to Critical
+        };
+
         public LogLevel CurrentLogLevel { get; private set; }
+
         public bool IsCliOverridden { get; private set; }
 
-        public void SetInitialLogLevel(LogLevel logLevel = LogLevel.Error, bool isCliOverridden = false)
+        public bool IsConfigOverridden { get; private set; }
+
+        public void SetInitialLogLevel(LogLevel logLevel = LogLevel.Error, bool isCliOverridden = false, bool isConfigOverridden = false)
         {
             CurrentLogLevel = logLevel;
             IsCliOverridden = isCliOverridden;
+            IsConfigOverridden = isConfigOverridden;
         }
 
         public void UpdateFromRuntimeConfig(RuntimeConfig runtimeConfig)
@@ -20,7 +46,52 @@ public void UpdateFromRuntimeConfig(RuntimeConfig runtimeConfig)
             if (!IsCliOverridden)
             {
                 CurrentLogLevel = runtimeConfig.GetConfiguredLogLevel();
+
+                // Track if config explicitly set a log level (not just using defaults)
+                IsConfigOverridden = !runtimeConfig.IsLogLevelNull();
+            }
+        }
+
+        /// <summary>
+        /// Updates the log level from an MCP logging/setLevel request.
+        /// Precedence (highest to lowest):
+        /// 1. CLI --LogLevel flag (IsCliOverridden = true)
+        /// 2. Config runtime.telemetry.log-level (IsConfigOverridden = true)
+        /// 3. MCP logging/setLevel
+        /// 
+        /// If CLI or Config overrode, this method accepts the request silently but does not change the level.
+        /// </summary>
+        /// <param name="mcpLevel">The MCP log level string (e.g., "debug", "info", "warning", "error").</param>
+        /// <returns>True if the level was changed; false if CLI/Config override prevented the change or level was invalid.</returns>
+        public bool UpdateFromMcp(string mcpLevel)
+        {
+            // If CLI overrode the log level, accept the request but don't change anything.
+            // This prevents MCP clients from getting errors, but CLI wins.
+            if (IsCliOverridden)
+            {
+                return false;
             }
+
+            // If Config explicitly set the log level, accept the request but don't change anything.
+            // Config has second precedence after CLI.
+            if (IsConfigOverridden)
+            {
+                return false;
+            }
+
+            if (string.IsNullOrWhiteSpace(mcpLevel))
+            {
+                return false;
+            }
+
+            if (_mcpLevelMapping.TryGetValue(mcpLevel, out LogLevel logLevel))
+            {
+                CurrentLogLevel = logLevel;
+                return true;
+            }
+
+            // Unknown level - don't change, but don't fail either
+            return false;
         }
 
         public bool ShouldLog(LogLevel logLevel)