Tools

Tools are the primary way to expose executable actions to an LLM. A tool is a Delphi method decorated with the [McpTool] attribute.

Defining a Tool Class

Register the class and use [McpTool] on the methods you want to expose:

unit Demo.HelpDeskService;

interface

uses
  System.SysUtils,
  MCPConnect.MCP.Attributes;

type
  THelpDeskService = class
  public
    // This method is published as an MCP tool
    [McpTool('doclist', 'List all the available documents')]
    function ListDocument(
      [McpParam('category', 'Document Category')] const ACategory: string
    ): TContentList;

    // This method is NOT exposed — it lacks the [McpTool] attribute
    procedure InternalStuff;
  end;

Methods without [McpTool] are completely invisible to the MCP protocol, so you can freely mix internal and public logic in the same class.

Organizing Tools with Scopes

When building larger MCP servers with multiple tool classes, assign a scope (namespace prefix) using the [McpScope] attribute. This avoids name conflicts and produces a cleaner API.

Why Use Scopes?

• Avoid conflicts — Multiple tool classes can have methods with the same name.
• Clear organization — Group related tools logically.
• Better API structure — Tools are exposed as scope_toolname (e.g., auth_login).

Defining a Scoped Tool Class

[McpScope('auth')]
TAuthService = class
public
  [McpTool('login', 'Authenticate user')]
  function Login([McpParam('username')] AUser: string): Boolean;

  [McpTool('logout', 'Logout user')]
  function Logout: Boolean;
end;

Exposed tool names will be auth_login and auth_logout.

Multiple Scoped Classes

[McpScope('auth')]    TAuthService   = class ... end;
[McpScope('tickets')] TTicketService = class ... end;
[McpScope('users')]   TUserService   = class ... end;

// Registration
FJRPCServer
  .Plugin.Configure<IMCPConfig>
    .Tools
      .RegisterClass(TAuthService)    // auth_login, auth_logout
      .RegisterClass(TTicketService)  // tickets_list, tickets_create
      .RegisterClass(TUserService)    // users_get, users_update
    .BackToMCP;

Important: Tool names must match the MCP pattern ^[a-zA-Z0-9_-]{1,64}$ (only alphanumeric, underscore, hyphen).

Tool Annotations

[McpTool] accepts an optional third string parameter for key-value annotations:

[McpTool('my_tool', 'Description', 'app=ui://my-app/index.html,category=demo')]
function MyTool: string;

Supported built-in annotations:

Key	Example	Meaning
app	app=ui://my-app/index.html	Links tool to an MCP App UI
disabled	disabled	Hides the tool from the tools list