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

Use [McpTool] on the methods you want to expose:

type
  THelpDeskService = class
  public
    [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.

Registering Tools

Tool classes are registered in the .Tools section of IMCPConfig:

.Tools
  .RegisterClass(TAuthService)
  .RegisterClass(TTicketService)
.BackToMCP

RegisterClass scans the class via RTTI and registers every method carrying [McpTool].

Registering Without Attributes

For classes that cannot carry Delphi custom attributes (e.g. compiled from C++ Builder), use the fluent RegisterTool API:

.Tools
  .RegisterTool(TMathTool, 'DoubleOrZero', 'double_or_zero',
    'Doubles or zeroes the value', 'icon=money.png')
    .WithParam('AValue', 'value', 'The value to process')
    .WithParam('ADouble', 'double', 'Whether to double it')
    .EndTool
.BackToMCP

• RegisterTool(AClass, AMethodName, AName, ADescription, ATags) — looks up AMethodName on AClass via RTTI and returns a builder. AName/ADescription/ATags work exactly like the corresponding [McpTool] arguments.
• WithParam(AParamName, AName, ADescription, ATags) — maps a Delphi parameter to its JSON-facing name. Every parameter must be covered, or EndTool raises an exception.
• EndTool — finalizes the tool and returns to the .Tools builder.

Both registration paths can be freely mixed in the same .Tools section.

Scopes

The [McpScope] attribute adds a namespace prefix to every tool name in a class, avoiding name conflicts when multiple classes expose tools with the same name:

[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. The separator is _ by default and can be changed via the SetScopeSeparator option in the Server configuration.

Note: MCPConnect does not enforce any restriction on tool names. However, the MCP specification recommends that tool names be 1–64 characters long, case-sensitive, and limited to alphanumeric characters, underscores (_), dashes (-), dots (.), and forward slashes (/).

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
icon	icon=money.png	Tool icon — a filename resolved against .Server.SetIconFolder(...), or a full scheme:// URL
category	category=finance	Free-form grouping label for the tool
readonly	readonly	Sets the readOnlyHint annotation
destructive	destructive	Sets the destructiveHint annotation
idempotent	idempotent	Sets the idempotentHint annotation
openworld	openworld	Sets the openWorldHint annotation
structured	structured	Also generates outputSchema/structuredContent from the method's return type, which must be a JSON object (a record or class, not an array/scalar)

Combine multiple tags with commas, e.g. 'app=ui://my-app/index.html,category=demo,readonly'.

Linking a Tool to an MCP App

A tool can declare that its result should be rendered by an MCP App in two equivalent ways:

Option A — separate [McpApp] attribute on the tool method:

[McpTool('get_tickets', 'List available tickets', 'icon=badge.png')]
[McpApp('ui://my-app/index.html')]
function GetTickets: TTickets;

Option B — app= annotation in the third parameter of [McpTool]:

[McpTool('get_tickets', 'List available tickets', 'app=ui://my-app/index.html')]
function GetTickets: TTickets;

Both tell the client that the tool result can be rendered inside the specified app UI.