Model context protocol server prompts with microsoft semantic kernel

This post focuses on implementing server prompts, a key feature of the Model Context Protocol (MCP) designed for reusable template definitions. We will explore how to implement these server prompts using both the MCP C# SDK and Semantic Kernel for enhanced templating capabilities. Further details on MCP server prompts can be found in the MCP documentation. MCP Server Prompts via MCP C# SDK Attributes MCP C# SDK allows for defining prompts through attributes. This method offers a direct implementation without requiring Semantic Kernel for basic string manipulation as the following example shows. [McpServerPromptType] internal sealed class StringFormatPrompt { private readonly string _format; private readonly ILogger _logger; public StringFormatPrompt(ILogger logger) { _logger = logger; _format = "Tell a joke about {0}."; } [McpServerPrompt(Name = "Joke"), Description("Tell a joke about a topic.")] public IReadOnlyCollection Format([Description("The topic of the joke.")] string topic) { _logger.LogInformation("Generating prompt with topic: {Topic}", topic); var content = string.Format(CultureInfo.InvariantCulture, _format, topic); return [ new (ChatRole.User, content) ]; } } // Register for the prompt var serverBuilder = builder.Services.AddMcpServer() .WithHttpTransport() .WithPrompts(); Semantic Kernel Templates as MCP Server Prompts Semantic Kernel provides templating capabilities through JSON/YAML, Handlebars, and Liquid formats, along with plugin support. These templates can be exposed as MCP prompts using the MCP C# SDK. Prompt Templates in Semantic Kernel Semantic Kernel templates are configured with PromptTemplateConfig, created by IPromptTemplateFactory implementations, and can be easily rendered with input variables for dynamic prompt generation. var templateConfig = new PromptTemplateConfig("Tell a joke about {{$topic}}."); IPromptTemplateFactory templateFactory = new KernelPromptTemplateFactory(); var template = templateFactory.Create(templateConfig); var text = await template.RenderAsync(kernel, new KernelArguments { { "topic", "cats" } }); Expose prompts as McpServerPrompt McpServerPrompt is the abstract base class that represents an MCP prompt we can implement. internal sealed class TemplateServerPrompt : McpServerPrompt { public TemplateServerPrompt(PromptTemplateConfig promptTemplateConfig, IPromptTemplateFactory? promptTemplateFactory, ILoggerFactory? loggerFactory) { promptTemplateFactory ??= new KernelPromptTemplateFactory(loggerFactory ?? NullLoggerFactory.Instance); _template = promptTemplateFactory.Create(promptTemplateConfig); // MCP prompt ProtocolPrompt = new() { Name = promptTemplateConfig.Name ?? _template.GetType().Name, Description = promptTemplateConfig.Description, Arguments = promptTemplateConfig.InputVariables .Select(inputVariable => new PromptArgument { Name = inputVariable.Name, Description = inputVariable.Description, Required = inputVariable.IsRequired }) .ToList(), }; } public override async ValueTask GetAsync(RequestContext request, CancellationToken cancellationToken = default) { KernelArguments? arguments = default; var dictionary = request.Params?.Arguments; if (dictionary is not null) { arguments = new (); foreach (var (key, value) in dictionary) { arguments[key] = value; } } var kernel = request.Services?.GetService() ?? new Kernel(); var text = await _template.RenderAsync(kernel, arguments, cancellationToken); return new GetPromptResult { Messages = [ new PromptMessage { Content = new Content { Text = text } } ] }; } } // Register for the prompt with DI and MCP server // builder.Services.AddSingleton(...) var serverBuilder = builder.Services.AddMcpServer() .WithHttpTransport(); serverBuilder.Services.AddSingleton(provider => provider.GetRequiredService()); Exposing AIFunction as McpServerPrompt The McpServerPrompt class provides a Create method to expose a Microsoft.Extensions.AI.AIFunction as an MCP server prompt. internal sealed class TemplateAIFunction : AIFunction { //... protected override async ValueTask InvokeCoreAsync(AIFunctionArguments arguments, CancellationToken cancellationToken) { KernelArguments kernelArguments = []; foreach (var argument in arguments) { kernelArgume

Apr 24, 2025 - 00:02

Model context protocol server prompts with microsoft semantic kernel

This post focuses on implementing server prompts, a key feature of the Model Context Protocol (MCP) designed for reusable template definitions. We will explore how to implement these server prompts using both the MCP C# SDK and Semantic Kernel for enhanced templating capabilities. Further details on MCP server prompts can be found in the MCP documentation.

MCP Server Prompts via MCP C# SDK Attributes

MCP C# SDK allows for defining prompts through attributes. This method offers a direct implementation without requiring Semantic Kernel for basic string manipulation as the following example shows.


[McpServerPromptType]
internal sealed class StringFormatPrompt
{
    private readonly string _format;
    private readonly ILogger _logger;

    public StringFormatPrompt(ILogger<StringFormatPrompt> logger)
    {
        _logger = logger;
        _format = "Tell a joke about {0}.";
    }

    [McpServerPrompt(Name = "Joke"), Description("Tell a joke about a topic.")]
    public IReadOnlyCollection<ChatMessage> Format([Description("The topic of the joke.")] string topic)
    {
        _logger.LogInformation("Generating prompt with topic: {Topic}", topic);
        var content = string.Format(CultureInfo.InvariantCulture, _format, topic);
        return [
            new (ChatRole.User, content)
        ];
    }
 }    

 // Register for the prompt
 var serverBuilder = builder.Services.AddMcpServer()
    .WithHttpTransport()
    .WithPrompts<StringFormatPrompt>();

Semantic Kernel Templates as MCP Server Prompts

Semantic Kernel provides templating capabilities through JSON/YAML, Handlebars, and Liquid formats, along with plugin support. These templates can be exposed as MCP prompts using the MCP C# SDK.

Prompt Templates in Semantic Kernel
Semantic Kernel templates are configured with PromptTemplateConfig, created by IPromptTemplateFactory implementations, and can be easily rendered with input variables for dynamic prompt generation.

var templateConfig = new PromptTemplateConfig("Tell a joke about {{$topic}}.");
IPromptTemplateFactory templateFactory = new KernelPromptTemplateFactory();
var template = templateFactory.Create(templateConfig);
var text = await template.RenderAsync(kernel,
    new KernelArguments
    {
        { "topic", "cats" }
    });

Expose prompts as McpServerPrompt
McpServerPrompt is the abstract base class that represents an MCP prompt we can implement.


internal sealed class TemplateServerPrompt : McpServerPrompt
{
    public TemplateServerPrompt(PromptTemplateConfig promptTemplateConfig, IPromptTemplateFactory? promptTemplateFactory, ILoggerFactory? loggerFactory)
    {
        promptTemplateFactory ??= new KernelPromptTemplateFactory(loggerFactory ?? NullLoggerFactory.Instance);
        _template = promptTemplateFactory.Create(promptTemplateConfig);

        // MCP prompt
        ProtocolPrompt = new()
        {
            Name = promptTemplateConfig.Name ?? _template.GetType().Name,
            Description = promptTemplateConfig.Description,
            Arguments = promptTemplateConfig.InputVariables
                .Select(inputVariable =>
                    new PromptArgument
                    {
                        Name = inputVariable.Name,
                        Description = inputVariable.Description,
                        Required = inputVariable.IsRequired
                    })
                .ToList(),
        };
    }

    public override async ValueTask<GetPromptResult> GetAsync(RequestContext<GetPromptRequestParams> request, CancellationToken cancellationToken = default)
    {
        KernelArguments? arguments = default;

        var dictionary = request.Params?.Arguments;
        if (dictionary is not null)
        {
            arguments = new ();
            foreach (var (key, value) in dictionary)
            {
                arguments[key] = value;
            }
        }

        var kernel = request.Services?.GetService<Kernel>() ?? new Kernel();
        var text = await _template.RenderAsync(kernel, arguments, cancellationToken);

        return 
            new GetPromptResult
            {
                Messages = [
                    new PromptMessage
                    {
                        Content = new Content { Text = text }
                    } 
            ]
        };
    }
}

// Register for the prompt with DI and MCP server
// builder.Services.AddSingleton(...)
var serverBuilder = builder.Services.AddMcpServer()
    .WithHttpTransport();
serverBuilder.Services.AddSingleton<McpServerPrompt>(provider => 
    provider.GetRequiredService<TemplateServerPrompt>());

Exposing AIFunction as McpServerPrompt
The McpServerPrompt class provides a Create method to expose a Microsoft.Extensions.AI.AIFunction as an MCP server prompt.


internal sealed class TemplateAIFunction : AIFunction 
{
    //...

    protected override async ValueTask<object?> InvokeCoreAsync(AIFunctionArguments arguments, CancellationToken cancellationToken)
    {
        KernelArguments kernelArguments = [];

        foreach (var argument in arguments)
        {
            kernelArguments[argument.Key] = argument.Value;
        }

        var kernel = arguments.Services?.GetService<Kernel>() ?? new Kernel();
        var text = await _template.RenderAsync(kernel, kernelArguments, cancellationToken);
        return text;
    }
}

// Register for the prompt with DI and MCP server
// builder.Services.AddSingleton(...)
var serverBuilder = builder.Services.AddMcpServer()
    .WithHttpTransport();
serverBuilder.Services.AddSingleton<McpServerPrompt>(provider => 
    McpServerPrompt.Create(provider.GetRequiredService<TemplateServerPrompt>()));

Complete sample code

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