Building an MCP Server in .NET for AI Tool Integration

What is MCP?

MCP (Model Context Protocol) is an open standard by Anthropic that lets AI models discover and call external tools via a JSON-RPC interface.

Tool Manifest Endpoint

[HttpGet("manifest")]
public IActionResult GetManifest() => Ok(new
{
    schema_version = "v1",
    name = "blog-engine",
    tools = new[]
    {
        new { name = "get_posts", description = "List published blog posts" },
        new { name = "create_post", description = "Create a new blog post" }
    }
});

Tool Execution Endpoint

[HttpPost("execute")]
public async Task<IActionResult> Execute([FromBody] McpRequest req)
{
    return req.Tool switch
    {
        "get_posts" => Ok(await _blog.GetPublishedAsync()),
        "create_post" => Ok(await _blog.CreateAsync(req.Parameters)),
        _ => BadRequest(new { error = "Unknown tool" })
    };
}

Conclusion

An MCP server turns your existing .NET APIs into AI-callable tools with minimal code. The protocol is simple JSON-RPC — no special SDK needed.