.NET: Support InvokeFunctionTool for declarative workflows

dotnet/Directory.Packages.props

@@ -111,10 +111,10 @@
     <!-- Identity -->
     <PackageVersion Include="Microsoft.Identity.Client.Extensions.Msal" Version="4.78.0" />
     <!-- Workflows -->
-    <PackageVersion Include="Microsoft.Agents.ObjectModel" Version="2026.2.2.1" />
-    <PackageVersion Include="Microsoft.Agents.ObjectModel.Json" Version="2026.2.2.1" />
-    <PackageVersion Include="Microsoft.Agents.ObjectModel.PowerFx" Version="2026.2.2.1" />
-    <PackageVersion Include="Microsoft.PowerFx.Interpreter" Version="1.5.0-build.20251008-1002" />
+    <PackageVersion Include="Microsoft.Agents.ObjectModel" Version="2026.2.3.1" />
+    <PackageVersion Include="Microsoft.Agents.ObjectModel.Json" Version="2026.2.3.1" />
+    <PackageVersion Include="Microsoft.Agents.ObjectModel.PowerFx" Version="2026.2.3.1" />
+    <PackageVersion Include="Microsoft.PowerFx.Interpreter" Version="1.8.1" />
     <!-- Durable Task -->
     <PackageVersion Include="Microsoft.DurableTask.Client" Version="1.18.0" />
     <PackageVersion Include="Microsoft.DurableTask.Client.AzureManaged" Version="1.18.0" />

dotnet/agent-framework-dotnet.slnx

@@ -215,6 +215,7 @@
     <Project Path="samples/GettingStarted/Workflows/Declarative/Marketing/Marketing.csproj" />
     <Project Path="samples/GettingStarted/Workflows/Declarative/StudentTeacher/StudentTeacher.csproj" />
     <Project Path="samples/GettingStarted/Workflows/Declarative/ToolApproval/ToolApproval.csproj" />
+    <Project Path="samples/GettingStarted/Workflows/Declarative/InvokeFunctionTool/InvokeFunctionTool.csproj" />
   </Folder>
   <Folder Name="/Samples/GettingStarted/Workflows/Declarative/Examples/">
     <File Path="../workflow-samples/CustomerSupport.yaml" />

dotnet/samples/GettingStarted/Workflows/Declarative/InvokeFunctionTool/InvokeFunctionTool.csproj

@@ -0,0 +1,38 @@
+<Project Sdk="Microsoft.NET.Sdk">
+
+  <PropertyGroup>
+    <OutputType>Exe</OutputType>
+    <TargetFrameworks>net10.0</TargetFrameworks>
+    <Nullable>enable</Nullable>
+    <ImplicitUsings>enable</ImplicitUsings>
+  </PropertyGroup>
+
+  <PropertyGroup>
+    <InjectIsExternalInitOnLegacy>true</InjectIsExternalInitOnLegacy>
+    <InjectSharedFoundryAgents>true</InjectSharedFoundryAgents>
+    <InjectSharedWorkflowsExecution>true</InjectSharedWorkflowsExecution>
+    <InjectSharedWorkflowsSettings>true</InjectSharedWorkflowsSettings>
+  </PropertyGroup>
+
+  <ItemGroup>
+    <PackageReference Include="Microsoft.Extensions.Configuration" />
+    <PackageReference Include="Microsoft.Extensions.Configuration.Binder" />
+    <PackageReference Include="Microsoft.Extensions.Configuration.EnvironmentVariables" />
+    <PackageReference Include="Microsoft.Extensions.Configuration.Json" />
+    <PackageReference Include="Microsoft.Extensions.Configuration.UserSecrets" />
+    <PackageReference Include="Microsoft.Extensions.DependencyInjection" />
+    <PackageReference Include="Microsoft.Extensions.Logging" />
+  </ItemGroup>
+
+  <ItemGroup>
+    <ProjectReference Include="..\..\..\..\..\src\Microsoft.Agents.AI.Workflows.Declarative\Microsoft.Agents.AI.Workflows.Declarative.csproj" />
+    <ProjectReference Include="..\..\..\..\..\src\Microsoft.Agents.AI.Workflows.Declarative.AzureAI\Microsoft.Agents.AI.Workflows.Declarative.AzureAI.csproj" />
+  </ItemGroup>
+
+  <ItemGroup>
+    <None Include="InvokeFunctionTool.yaml">
+      <CopyToOutputDirectory>Always</CopyToOutputDirectory>
+    </None>
+  </ItemGroup>
+
+</Project>

dotnet/samples/GettingStarted/Workflows/Declarative/InvokeFunctionTool/InvokeFunctionTool.yaml

@@ -0,0 +1,55 @@
+#
+# This workflow demonstrates using InvokeFunctionTool to call functions directly
+# from the workflow without going through an AI agent first.
+#
+# InvokeFunctionTool allows workflows to:
+# - Pre-fetch data before calling an AI agent
+# - Execute operations directly without AI involvement
+# - Store function results in workflow variables for later use
+#
+# Example input: 
+# What are the specials in the menu?
+#
+kind: Workflow
+trigger:
+
+  kind: OnConversationStart
+  id: workflow_invoke_function_tool_demo
+  actions:
+
+    # Invoke GetSpecials function to get today's specials directly from the workflow
+    - kind: InvokeFunctionTool
+      id: invoke_get_specials
+      conversationId: =System.ConversationId
+      requireApproval: true
+      functionName: GetSpecials
+      output:
+        autoSend: true
+        result: Local.Specials
+        messages: Local.FunctionMessage
+
+    # Display a message showing we retrieved the specials
+    - kind: SendMessage
+      id: show_specials_intro
+      message: "Today's specials have been retrieved. Here they are: {Local.Specials}"
+
+    # Now use an agent to format and present the specials to the user
+    - kind: InvokeAzureAgent
+      id: invoke_menu_agent
+      conversationId: =System.ConversationId
+      agent:
+        name: FunctionMenuAgent
+      input:
+        messages: =UserMessage("Please describe today's specials in an appealing way.")
+      output:
+        messages: Local.AgentResponse
+
+    # Allow the user to ask follow-up questions in a loop
+    - kind: InvokeAzureAgent
+      id: invoke_followup
+      conversationId: =System.ConversationId
+      agent:
+        name: FunctionMenuAgent
+      input:
+        externalLoop:
+          when: =Upper(System.LastMessage.Text) <> "EXIT"

dotnet/samples/GettingStarted/Workflows/Declarative/InvokeFunctionTool/MenuPlugin.cs

@@ -0,0 +1,85 @@
+// Copyright (c) Microsoft. All rights reserved.
+
+using System.ComponentModel;
+
+namespace Demo.Workflows.Declarative.InvokeFunctionTool;
+
+#pragma warning disable CA1822 // Mark members as static
+
+/// <summary>
+/// Plugin providing menu-related functions that can be invoked directly by the workflow
+/// using the InvokeFunctionTool action.
+/// </summary>
+public sealed class MenuPlugin
+{
+    [Description("Provides a list items on the menu.")]
+    public MenuItem[] GetMenu()
+    {
+        return s_menuItems;
+    }
+
+    [Description("Provides a list of specials from the menu.")]
+    public MenuItem[] GetSpecials()
+    {
+        return [.. s_menuItems.Where(i => i.IsSpecial)];
+    }
+
+    [Description("Provides the price of the requested menu item.")]
+    public float? GetItemPrice(
+        [Description("The name of the menu item.")]
+        string name)
+    {
+        return s_menuItems.FirstOrDefault(i => i.Name.Equals(name, StringComparison.OrdinalIgnoreCase))?.Price;
+    }
+
+    private static readonly MenuItem[] s_menuItems =
+        [
+            new()
+            {
+                Category = "Soup",
+                Name = "Clam Chowder",
+                Price = 4.95f,
+                IsSpecial = true,
+            },
+            new()
+            {
+                Category = "Soup",
+                Name = "Tomato Soup",
+                Price = 4.95f,
+                IsSpecial = false,
+            },
+            new()
+            {
+                Category = "Salad",
+                Name = "Cobb Salad",
+                Price = 9.99f,
+            },
+            new()
+            {
+                Category = "Salad",
+                Name = "House Salad",
+                Price = 4.95f,
+            },
+            new()
+            {
+                Category = "Drink",
+                Name = "Chai Tea",
+                Price = 2.95f,
+                IsSpecial = true,
+            },
+            new()
+            {
+                Category = "Drink",
+                Name = "Soda",
+                Price = 1.95f,
+            },
+        ];
+
+    public sealed class MenuItem
+    {
+        public string Category { get; init; } = string.Empty;
+        public string Name { get; init; } = string.Empty;
+        public float Price { get; init; }
+        public bool IsSpecial { get; init; }
+    }
+}

dotnet/samples/GettingStarted/Workflows/Declarative/InvokeFunctionTool/Program.cs

@@ -0,0 +1,88 @@
+// Copyright (c) Microsoft. All rights reserved.
+
+using Azure.AI.Projects;
+using Azure.AI.Projects.OpenAI;
+using Azure.Identity;
+using Microsoft.Extensions.AI;
+using Microsoft.Extensions.Configuration;
+using OpenAI.Responses;
+using Shared.Foundry;
+using Shared.Workflows;
+
+namespace Demo.Workflows.Declarative.InvokeFunctionTool;
+
+/// <summary>
+/// Demonstrate a workflow that uses InvokeFunctionTool to call functions directly
+/// from the workflow without going through an AI agent first.
+/// </summary>
+/// <remarks>
+/// The InvokeFunctionTool action allows workflows to invoke function tools directly,
+/// enabling pre-fetching of data or executing operations before calling an AI agent.
+/// See the README.md file in the parent folder (../README.md) for detailed
+/// information about the configuration required to run this sample.
+/// </remarks>
+internal sealed class Program
+{
+    public static async Task Main(string[] args)
+    {
+        // Initialize configuration
+        IConfiguration configuration = Application.InitializeConfig();
+        Uri foundryEndpoint = new(configuration.GetValue(Application.Settings.FoundryEndpoint));
+
+        // Create the menu plugin with functions that can be invoked directly by the workflow
+        MenuPlugin menuPlugin = new();
+        AIFunction[] functions =
+            [
+                AIFunctionFactory.Create(menuPlugin.GetMenu),
+                AIFunctionFactory.Create(menuPlugin.GetSpecials),
+                AIFunctionFactory.Create(menuPlugin.GetItemPrice),
+            ];
+
+        // Ensure sample agent exists in Foundry
+        await CreateAgentAsync(foundryEndpoint, configuration);
+
+        // Get input from command line or console
+        string workflowInput = Application.GetInput(args);
+
+        // Create the workflow factory.
+        WorkflowFactory workflowFactory = new("InvokeFunctionTool.yaml", foundryEndpoint);
+
+        // Execute the workflow
+        WorkflowRunner runner = new(functions) { UseJsonCheckpoints = true };
+        await runner.ExecuteAsync(workflowFactory.CreateWorkflow, workflowInput);
+    }
+
+    private static async Task CreateAgentAsync(Uri foundryEndpoint, IConfiguration configuration)
+    {
+        // WARNING: DefaultAzureCredential is convenient for development but requires careful consideration in production.
+        AIProjectClient aiProjectClient = new(foundryEndpoint, new DefaultAzureCredential());
+
+        await aiProjectClient.CreateAgentAsync(
+            agentName: "FunctionMenuAgent",
+            agentDefinition: DefineMenuAgent(configuration, []), // Create Agent with no function tool in the definition.
+            agentDescription: "Provides information about the restaurant menu");
+    }
+
+    private static PromptAgentDefinition DefineMenuAgent(IConfiguration configuration, AIFunction[] functions)
+    {
+        PromptAgentDefinition agentDefinition =
+            new(configuration.GetValue(Application.Settings.FoundryModelMini))
+            {
+                Instructions =
+                    """
+                    Answer the users questions about the menu.
+                    Use the information provided in the conversation history to answer questions.
+                    If the information is already available in the conversation, use it directly.
+                    For questions or input that do not require searching the documentation, inform the
+                    user that you can only answer questions about what's on the menu.
+                    """
+            };
+
+        foreach (AIFunction function in functions)
+        {
+            agentDefinition.Tools.Add(function.AsOpenAIResponseTool());
+        }
+
+        return agentDefinition;
+    }
+}

dotnet/src/Microsoft.Agents.AI.Workflows.Declarative/Interpreter/WorkflowActionVisitor.cs

@@ -390,6 +390,27 @@ protected override void Visit(InvokeAzureAgent item)
         this._workflowModel.AddNode(new DelegateActionExecutor(postId, this._workflowState, action.CompleteAsync), action.ParentId);
     }
 
+    protected override void Visit(InvokeFunctionTool item)
+    {
+        this.Trace(item);
+
+        // Entry point to invoke function tool - always yields for external execution
+        InvokeFunctionToolExecutor action = new(item, this._workflowOptions.AgentProvider, this._workflowState);
+        this.ContinueWith(action);
+
+        // Define request-port for function tool invocation (always requires external input)
+        string externalInputPortId = InvokeFunctionToolExecutor.Steps.ExternalInput(action.Id);
+        RequestPortAction externalInputPort = new(RequestPort.Create<ExternalInputRequest, ExternalInputResponse>(externalInputPortId));
+        this._workflowModel.AddNode(externalInputPort, action.ParentId);
+        this._workflowModel.AddLinkFromPeer(action.ParentId, externalInputPortId);
+
+        // Capture response when external input is received
+        string resumeId = InvokeFunctionToolExecutor.Steps.Resume(action.Id);
+        this.ContinueWith(
+            new DelegateActionExecutor<ExternalInputResponse>(resumeId, this._workflowState, action.CaptureResponseAsync),
+            action.ParentId);
+    }
+
     protected override void Visit(InvokeAzureResponse item)
     {
         this.NotSupported(item);

dotnet/src/Microsoft.Agents.AI.Workflows.Declarative/Interpreter/WorkflowTemplateVisitor.cs

@@ -365,6 +365,8 @@ protected override void Visit(SendActivity item)
 
     #region Not supported
 
+    protected override void Visit(InvokeFunctionTool item) => this.NotSupported(item);
+
     protected override void Visit(AnswerQuestionWithAI item) => this.NotSupported(item);
 
     protected override void Visit(DeleteActivity item) => this.NotSupported(item);