mars-mcp-server

Build an MCP server with MARS-Curiosity

MARS ships native MCP support (units MARS.MCP.* in Source/): derive a resource from TMCPResource, mark methods with [MCPTool], and any MARS server becomes an MCP server speaking the Streamable HTTP transport (single endpoint, JSON-RPC 2.0 over POST). Tool list and JSON Schema are generated from RTTI — no protocol code to write.

The complete working example is Demos/MCPServer in the MARS repository (public tools + FireDAC-backed authenticated tools + OAuth).

Minimal MCP server

unit Server.Resources.MCP;

interface

uses
  SysUtils, Classes
, MARS.Core.Attributes, MARS.Core.MediaType
, MARS.MCP.Resource, MARS.MCP.Attributes;

type
  TCalculationResult = record
    operation: string;
    value: Double;
  end;

  [Path('mcp')
  , MCPServerInfo('My MCP Server', '1.0.0'
    , 'Optional instructions the AI agent reads on connection.')]
  TMyMCPResource = class(TMCPResource)
  public
    [MCPTool('say_hello', 'Returns a friendly greeting for the given name')]
    function SayHello(
      [MCPParam('name', 'Name of the person to greet')] const AName: string): string;

    [MCPTool('add_numbers', 'Adds two numbers and returns a structured result')]
    function AddNumbers(
      [MCPParam('a', 'First operand')] const A: Double;
      [MCPParam('b', 'Second operand')] const B: Double): TCalculationResult;
  end;

implementation

uses
  MARS.Core.Registry;

function TMyMCPResource.SayHello(const AName: string): string;
begin
  Result := 'Hello, ' + AName + '!';
end;

function TMyMCPResource.AddNumbers(const A, B: Double): TCalculationResult;
begin
  Result.operation := 'add';
  Result.value := A + B;
end;

initialization
  MARSRegister([TMyMCPResource]);

end.

This is a regular MARS resource: register the unit mask in Server.Ignition.pas as usual (AddApplication('DefaultApp', '/default', ['Server.Resources.*'])). The MCP endpoint is the composed URL, e.g. http://localhost:8080/rest/default/mcp. Everything the mars-development skill says about resources, [Context] injection and configuration applies here too.