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CrestApps.AgentSkills.Mcp

A generic, reusable MCP (Model Context Protocol) engine that discovers and exposes Agent Skills as MCP Prompts and Resources. Built on the MCP C# SDK.

For Orchard Core–specific skills, see the companion package CrestApps.AgentSkills.Mcp.OrchardCore, which builds on top of this project and bundles Orchard Core skills.

Install

dotnet add package CrestApps.AgentSkills.Mcp

Usage

Register Skills with an MCP Server

builder.Services.AddMcpServer(mcp =>
{
    mcp.AddAgentSkills();
});

Register Services Only (No Eager Loading)

To register the skill services in DI without eagerly loading them:

builder.Services.AddAgentSkillServices();

The consumer is then responsible for resolving IMcpPromptProvider and IMcpResourceProvider and attaching them to the MCP server.

With Custom Path

builder.Services.AddMcpServer(mcp =>
{
    mcp.AddAgentSkills(options =>
    {
        options.Path = "./my-skills";
    });
});

Resolving Providers from DI

The file store and providers are registered as singletons and can be injected:

public sealed class MyService
{
    private readonly IMcpPromptProvider _promptProvider;
    private readonly IMcpResourceProvider _resourceProvider;

    public MyService(
        IMcpPromptProvider promptProvider,
        IMcpResourceProvider resourceProvider)
    {
        _promptProvider = promptProvider;
        _resourceProvider = resourceProvider;
    }

    public async Task ListPromptsAsync()
    {
        var prompts = await _promptProvider.GetPromptsAsync();
        // ...
    }
}

Supported Skill Formats

Skills are discovered from subdirectories under the configured skills path. Each skill directory must contain one of the following skill definition files:

Markdown (.md)

A SKILL.md file with YAML front-matter:

---
name: my-skill
description: A description of my skill.
---
# Prompt content

This is the body that becomes the MCP prompt.

YAML (.yaml / .yml)

A SKILL.yaml or SKILL.yml file:

name: my-skill
description: A description of my skill.
body: |
  # Prompt content
  This is the body that becomes the MCP prompt.

Required Fields

Both formats require:

Field Description
name Unique skill identifier
description Human-readable description

The body field (or Markdown body after front-matter) provides the prompt content.

Reference Files

Each skill directory may include a references/ subdirectory containing additional .md files. These are exposed as MCP Resources:

.agents/skills/
  my-skill/
    SKILL.md          (or SKILL.yaml / SKILL.yml)
    references/
      example1.md
      example2.md

Links

What Gets Exposed

MCP Type Source Description
Prompts Skill file body content Prompt templates from SKILL.md body or SKILL.yaml body field
Resources Skill files Full skill file content (metadata + body)
Resources references/*.md files Additional reference documents for each skill

Architecture

Services

Service Lifetime Purpose
IAgentSkillFilesStore Singleton Abstraction for skill file access
IMcpPromptProvider Singleton Reads skill files → cached McpServerPrompt instances
IMcpResourceProvider Singleton Reads skill + reference files → cached McpServerResource instances

Parsers

Parser Formats Purpose
SkillFrontMatterParser .md Parses YAML front-matter from Markdown files
SkillYamlParser .yaml, .yml Parses YAML skill definitions
SkillFileParser All Unified parser that detects format and delegates

How It Works

  1. Place skill directories under .agents/skills/ (or a custom path).
  2. Each skill directory contains a SKILL.md, SKILL.yaml, or SKILL.yml file.
  3. AddAgentSkills() registers IAgentSkillFilesStore, IMcpPromptProvider, and IMcpResourceProvider as singletons.
  4. At runtime, providers discover skill files, parse metadata, and create MCP prompts/resources.
  5. Results are cached after the first call for optimal performance.
  6. MCP clients can discover and use these prompts and resources via the MCP protocol.

Development

Build

dotnet build

Run Tests

dotnet test

Validate Skills Locally

Place your skill files in a directory and use the test infrastructure:

var fileStore = new PhysicalSkillFileStore("/path/to/skills");
var provider = new SkillPromptProvider(fileStore, NullLogger<SkillPromptProvider>.Instance);
var prompts = await provider.GetPromptsAsync();

Relationship to Other Packages

CrestApps.AgentSkills.Mcp              ← Generic, reusable MCP engine (this package)

This is the base package that other skill distribution packages can build upon.

Requirements

  • .NET 10.0+
  • MCP C# SDK (ModelContextProtocol NuGet package)
  • An MCP server host (e.g., ASP.NET Core with ModelContextProtocol.AspNetCore)

License

This project is licensed under the MIT License.