MCP protocol

MCP is an explicit server protocol that exposes selected AnyProtocol contract methods as Model Context Protocol tools. A method is published only when it has the [McpTool] attribute; selecting MCP does not expose every contract method automatically.

Install

dotnet add package AnyProtocol.Mcp.AspNetCore

HTTP endpoint

builder.Services.AddAnyProtocol(link => link
    .UseSerializer(new TextJsonMessageSerializer())
        .AddServer<IOrders, Orders>(server => server.UseProtocols(ProtocolKey.Mcp)));
builder.Services.AddAnyProtocolMcp();
// Configure a real application scheme; this example uses JWT bearer authentication.
builder.Services.AddAuthentication().AddJwtBearer();
builder.Services.AddAuthorization();

var app = builder.Build();
app.UseAuthentication();
app.UseAuthorization();
app.MapAnyProtocolMcp("/mcp");
await app.RunAsync();

Mark only the operations intended for tool discovery:

[Channel("orders")]
public interface IOrders
{
    [Idempotent]
    [McpTool(
        Name = "orders_get",
        Description = "Reads an order by identifier.",
        ReadOnly = true)]
    ValueTask<Order> GetAsync(
        GetOrderRequest request,
        CancellationToken cancellationToken);
}

public sealed record GetOrderRequest(string OrderId);
public sealed record Order(string Id, string Status);

Put McpTool on the contract interface method. MCP compiles its catalog from the contract descriptor; putting the attribute only on an implementation method does not select the operation. The input request must serialize to a JSON object, so use a request DTO/record (or EmptyRequest for a no-input tool) rather than a scalar parameter.

For process integrations, use AddAnyProtocolMcpStdio() instead of the HTTP registration and mapping.

Important behavior

  • MCP is a server exposure protocol; it is not a client transport.
  • Startup validation requires the MCP adapter to be registered and its endpoint to be mapped.
  • Contract methods without [McpTool] are not exposed.
  • Tool names are optional; the default is a bounded snake_case name derived from the contract and method. Explicit names must be 1–128 ASCII letters, digits, ., _, or -.
  • Server-streaming methods cannot be published as MCP tools. Tool input schemas must be objects; non-object output values are wrapped as an object result.
  • ReadOnly, Destructive, Idempotent, and OpenWorld are client-facing metadata hints. Authorization, validation, and side-effect controls remain host responsibilities.
  • HTTP MCP endpoints require ASP.NET Core authorization by default. Configure authentication, register the required policy, and call UseAuthorization() before serving requests.
  • MapAnyProtocolMcpAllowAnonymousForDevelopment() is an explicitly named local-development opt-out; never use it for an internet-facing endpoint. Stdio has a separate process boundary.

See Security and Getting started for endpoint and contract setup.

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