Class McpToolAttribute

Marks a static method or class as an MCP tool that can be invoked by MCP clients. Tools are automatically discovered at editor startup using Unity's TypeCache system.

Inheritance
object
Attribute
McpToolAttribute
Implements
Inherited Members
Namespace: Unity.AI.MCP.Editor.ToolRegistry
Assembly: Unity.AI.MCP.Editor.dll
Syntax
[AttributeUsage(AttributeTargets.Class|AttributeTargets.Method, AllowMultiple = false)]
public class McpToolAttribute : Attribute, _Attribute
Remarks

This attribute can be applied to:

  1. Static methods with 0-1 parameters (method-based tools)
  2. Classes implementing IUnityMcpTool or IUnityMcpTool<TParams> (class-based tools)

Method-based tools:

  • Must be public static
  • Can have 0 parameters, 1 typed parameter, or 1 JObject parameter
  • Schemas auto-generated for typed parameters
  • Use [McpSchema] attribute for custom schemas with JObject parameters

Class-based tools:

  • Must have a public parameterless constructor
  • Instantiated once at discovery time
  • Useful when tools need state or complex initialization

Tool names must be unique across the project. Duplicate names will generate warnings.

Examples

Method-based tool with typed parameters:

public class MyParams
{
    public string Name { get; set; }
}

[McpTool("my_tool", "Does something useful")]
public static object MyTool(MyParams params)
{
return new { result = $"Hello " };
}

Class-based tool:

[McpTool("stateful_tool", "Tool with state")]
public class StatefulTool : IUnityMcpTool<MyParams>
{
    private int callCount = 0;

public object Execute(MyParams parameters)
{
    callCount++;
    return new { calls = callCount };
}



}

Constructors

McpToolAttribute(string, string, string, object)

Creates an MCP tool attribute to mark a method or class as a discoverable tool.

Declaration
public McpToolAttribute(string name, string description = null, string title = null, object annotations = null)
Parameters
Type Name Description
string name

The unique name of the tool as exposed to MCP clients (use snake_case)
string description

Human-readable description of what the tool does. If null, defaults to the tool name
string title

Optional display title. If null, defaults to the description
object annotations

Optional MCP annotations object describing tool characteristics
Exceptions
Type Condition
ArgumentException

Thrown if name is null or empty

Properties

Annotations

Gets or sets optional MCP annotations describing tool behavior. Annotations can provide hints to clients about tool characteristics (e.g., side effects, cost).

Declaration
public object Annotations { get; set; }
Property Value
Type Description
object

Description

Gets the description of what the tool does. This description is sent to MCP clients and may be used by AI models to understand tool purpose.

Declaration
public string Description { get; }
Property Value
Type Description
string

EnabledByDefault

Gets or sets whether this tool is enabled by default when no user override exists. Tools with this set to true are part of the curated default set shown as enabled in the settings UI. New or unvalidated tools should leave this as false.

Declaration
public bool EnabledByDefault { get; set; }
Property Value
Type Description
bool

Groups

Gets or sets category tags for organizing and filtering tools. Use string identifiers from ToolCategory enum (e.g., "scripting", "scene", "assets").

Declaration
public string[] Groups { get; set; }
Property Value
Type Description
string[]

Name

Gets the unique name of the tool as exposed to MCP clients. Tool names should use snake_case convention (e.g., "my_tool", "read_file").

Declaration
public string Name { get; }
Property Value
Type Description
string

Title

Gets the display title of the tool (optional). If not specified, the Description is used as the title.

Declaration
public string Title { get; }
Property Value
Type Description
string

Implements