Expose workflow as MCP Tool

dotnet/src/Microsoft.Agents.AI.Hosting.AzureFunctions/BuiltInFunctionExecutor.cs

@@ -167,6 +167,18 @@ internal sealed class BuiltInFunctionExecutor : IFunctionExecutor
             return;
         }
 
+        if (context.FunctionDefinition.EntryPoint == BuiltInFunctions.RunWorkflowMcpToolFunctionEntryPoint)
+        {
+            if (mcpToolInvocationContext is null)
+            {
+                throw new InvalidOperationException($"MCP tool invocation context binding is missing for the invocation {context.InvocationId}.");
+            }
+
+            context.GetInvocationResult().Value =
+                await BuiltInFunctions.RunWorkflowMcpToolAsync(mcpToolInvocationContext, durableTaskClient, context);
+            return;
+        }
+
         throw new InvalidOperationException($"Unsupported function entry point '{context.FunctionDefinition.EntryPoint}' for invocation {context.InvocationId}.");
     }
 

dotnet/src/Microsoft.Agents.AI.Hosting.AzureFunctions/BuiltInFunctions.cs

@@ -29,6 +29,7 @@ internal static class BuiltInFunctions
     internal static readonly string InvokeWorkflowActivityFunctionEntryPoint = $"{typeof(BuiltInFunctions).FullName!}.{nameof(InvokeWorkflowActivityAsync)}";
     internal static readonly string GetWorkflowStatusHttpFunctionEntryPoint = $"{typeof(BuiltInFunctions).FullName!}.{nameof(GetWorkflowStatusAsync)}";
     internal static readonly string RespondToWorkflowHttpFunctionEntryPoint = $"{typeof(BuiltInFunctions).FullName!}.{nameof(RespondToWorkflowAsync)}";
+    internal static readonly string RunWorkflowMcpToolFunctionEntryPoint = $"{typeof(BuiltInFunctions).FullName!}.{nameof(RunWorkflowMcpToolAsync)}";
 
 #pragma warning disable IL3000 // Avoid accessing Assembly file path when publishing as a single file - Azure Functions does not use single-file publishing
     internal static readonly string ScriptFile = Path.GetFileName(typeof(BuiltInFunctions).Assembly.Location);
@@ -378,6 +379,39 @@ internal static class BuiltInFunctions
         return agentResponse.Text;
     }
 
+    /// <summary>
+    /// Runs a workflow via MCP tool trigger.
+    /// Extracts the <c>input</c> argument, schedules a new orchestration, waits for completion, and returns the output.
+    /// </summary>
+    public static async Task<string?> RunWorkflowMcpToolAsync(
+        [McpToolTrigger("BuiltInWorkflowMcpTool")] ToolInvocationContext context,
+        [DurableClient] DurableTaskClient client,
+        FunctionContext functionContext)
+    {
+        if (context.Arguments is null)
+        {
+            throw new ArgumentException("MCP Tool invocation is missing required arguments.");
+        }
+
+        if (!context.Arguments.TryGetValue("input", out object? inputObj) || inputObj is not string input)
+        {
+            throw new ArgumentException("MCP Tool invocation is missing required 'input' argument of type string.");
+        }
+
+        string workflowName = context.Name;
+        string orchestrationFunctionName = WorkflowNamingHelper.ToOrchestrationFunctionName(workflowName);
+
+        DurableWorkflowInput<string> orchestrationInput = new() { Input = input };
+        string instanceId = await client.ScheduleNewOrchestrationInstanceAsync(orchestrationFunctionName, orchestrationInput);
+
+        OrchestrationMetadata? metadata = await client.WaitForInstanceCompletionAsync(
+            instanceId,
+            getInputsAndOutputs: true,
+            cancellation: functionContext.CancellationToken);
+
+        return metadata?.ReadOutputAs<DurableWorkflowResult>()?.Result;
+    }
+
     /// <summary>
     /// Creates an error response with the specified status code and error message.
     /// </summary>

dotnet/src/Microsoft.Agents.AI.Hosting.AzureFunctions/CHANGELOG.md

@@ -2,6 +2,7 @@
 
 ## [Unreleased]
 
+- Added MCP tool trigger support for durable workflows
 - Added Azure Functions hosting support for durable workflows ([#4436](https://github.com/microsoft/agent-framework/pull/4436))
 
 ## v1.0.0-preview.251219.1

dotnet/src/Microsoft.Agents.AI.Hosting.AzureFunctions/FunctionMetadataFactory.cs

@@ -98,4 +98,27 @@ internal static class FunctionMetadataFactory
             ScriptFile = BuiltInFunctions.ScriptFile,
         };
     }
+
+    /// <summary>
+    /// Creates function metadata for an MCP tool trigger function that starts a workflow.
+    /// </summary>
+    /// <param name="workflowName">The name of the workflow to expose as an MCP tool.</param>
+    /// <param name="description">An optional description for the MCP tool. If null, a default description is generated.</param>
+    /// <returns>A <see cref="DefaultFunctionMetadata"/> configured for an MCP tool trigger.</returns>
+    internal static DefaultFunctionMetadata CreateWorkflowMcpToolTrigger(string workflowName, string? description)
+    {
+        return new DefaultFunctionMetadata
+        {
+            Name = $"{BuiltInFunctions.McpToolPrefix}{workflowName}",
+            Language = "dotnet-isolated",
+            RawBindings =
+            [
+                $$"""{"name":"context","type":"mcpToolTrigger","direction":"In","toolName":"{{workflowName}}","description":"{{description ?? $"Run the {workflowName} workflow"}}","toolProperties":"[{\"propertyName\":\"input\",\"propertyType\":\"string\",\"description\":\"The input to the workflow.\",\"isRequired\":true,\"isArray\":false}]"}""",
+                """{"name":"input","type":"mcpToolProperty","direction":"In","propertyName":"input","description":"The input to the workflow","isRequired":true,"dataType":"String","propertyType":"string"}""",
+                """{"name":"client","type":"durableClient","direction":"In"}"""
+            ],
+            EntryPoint = BuiltInFunctions.RunWorkflowMcpToolFunctionEntryPoint,
+            ScriptFile = BuiltInFunctions.ScriptFile,
+        };
+    }
 }

dotnet/src/Microsoft.Agents.AI.Hosting.AzureFunctions/FunctionsApplicationBuilderExtensions.cs

@@ -107,7 +107,8 @@ public static class FunctionsApplicationBuilderExtensions
             string.Equals(context.FunctionDefinition.EntryPoint, BuiltInFunctions.RunWorkflowOrchestrationFunctionEntryPoint, StringComparison.Ordinal) ||
             string.Equals(context.FunctionDefinition.EntryPoint, BuiltInFunctions.InvokeWorkflowActivityFunctionEntryPoint, StringComparison.Ordinal) ||
             string.Equals(context.FunctionDefinition.EntryPoint, BuiltInFunctions.GetWorkflowStatusHttpFunctionEntryPoint, StringComparison.Ordinal) ||
-            string.Equals(context.FunctionDefinition.EntryPoint, BuiltInFunctions.RespondToWorkflowHttpFunctionEntryPoint, StringComparison.Ordinal)
+            string.Equals(context.FunctionDefinition.EntryPoint, BuiltInFunctions.RespondToWorkflowHttpFunctionEntryPoint, StringComparison.Ordinal) ||
+            string.Equals(context.FunctionDefinition.EntryPoint, BuiltInFunctions.RunWorkflowMcpToolFunctionEntryPoint, StringComparison.Ordinal)
         );
         builder.Services.TryAddSingleton<BuiltInFunctionExecutor>();
     }

dotnet/src/Microsoft.Agents.AI.Hosting.AzureFunctions/FunctionsDurableOptions.cs

@@ -10,6 +10,7 @@ namespace Microsoft.Agents.AI.Hosting.AzureFunctions;
 internal sealed class FunctionsDurableOptions : DurableOptions
 {
     private readonly HashSet<string> _statusEndpointWorkflows = new(StringComparer.OrdinalIgnoreCase);
+    private readonly HashSet<string> _mcpToolTriggerWorkflows = new(StringComparer.OrdinalIgnoreCase);
 
     /// <summary>
     /// Enables the status HTTP endpoint for the specified workflow.
@@ -26,4 +27,20 @@ internal sealed class FunctionsDurableOptions : DurableOptions
     {
         return this._statusEndpointWorkflows.Contains(workflowName);
     }
+
+    /// <summary>
+    /// Enables the MCP tool trigger for the specified workflow.
+    /// </summary>
+    internal void EnableMcpToolTrigger(string workflowName)
+    {
+        this._mcpToolTriggerWorkflows.Add(workflowName);
+    }
+
+    /// <summary>
+    /// Returns whether the MCP tool trigger is enabled for the specified workflow.
+    /// </summary>
+    internal bool IsMcpToolTriggerEnabled(string workflowName)
+    {
+        return this._mcpToolTriggerWorkflows.Contains(workflowName);
+    }
 }

dotnet/src/Microsoft.Agents.AI.Hosting.AzureFunctions/Workflows/DurableWorkflowOptionsExtensions.cs

@@ -27,4 +27,31 @@ public static class DurableWorkflowOptionsExtensions
             functionsOptions.EnableStatusEndpoint(workflow.Name!);
         }
     }
+
+    /// <summary>
+    /// Adds a workflow and optionally exposes a status HTTP endpoint and/or an MCP tool trigger.
+    /// </summary>
+    /// <param name="options">The workflow options to add the workflow to.</param>
+    /// <param name="workflow">The workflow instance to add.</param>
+    /// <param name="exposeStatusEndpoint">If <see langword="true"/>, a GET endpoint is generated at <c>workflows/{name}/status/{runId}</c>.</param>
+    /// <param name="exposeMcpToolTrigger">If <see langword="true"/>, an MCP tool trigger is generated for the workflow.</param>
+    public static void AddWorkflow(this DurableWorkflowOptions options, Workflow workflow, bool exposeStatusEndpoint, bool exposeMcpToolTrigger)
+    {
+        ArgumentNullException.ThrowIfNull(options);
+
+        options.AddWorkflow(workflow);
+
+        if (options.ParentOptions is FunctionsDurableOptions functionsOptions)
+        {
+            if (exposeStatusEndpoint)
+            {
+                functionsOptions.EnableStatusEndpoint(workflow.Name!);
+            }
+
+            if (exposeMcpToolTrigger)
+            {
+                functionsOptions.EnableMcpToolTrigger(workflow.Name!);
+            }
+        }
+    }
 }

dotnet/src/Microsoft.Agents.AI.Hosting.AzureFunctions/Workflows/DurableWorkflowsFunctionMetadataTransformer.cs

@@ -113,6 +113,17 @@ internal sealed class DurableWorkflowsFunctionMetadataTransformer : IFunctionMet
                 }
             }
 
+            // Register an MCP tool trigger if opted in via AddWorkflow(exposeMcpToolTrigger: true).
+            if (this._options.IsMcpToolTriggerEnabled(workflow.Key))
+            {
+                string mcpToolFunctionName = $"{BuiltInFunctions.McpToolPrefix}{workflow.Key}";
+                if (registeredFunctions.Add(mcpToolFunctionName))
+                {
+                    this._logger.LogRegisteringWorkflowTrigger(workflow.Key, mcpToolFunctionName, "mcpTool");
+                    original.Add(FunctionMetadataFactory.CreateWorkflowMcpToolTrigger(workflow.Key, workflow.Value.Description));
+                }
+            }
+
             // Register activity or entity functions for each executor in the workflow.
             // ReflectExecutors() returns all executors across the graph; no need to manually traverse edges.
             foreach (KeyValuePair<string, ExecutorBinding> entry in workflow.Value.ReflectExecutors())