Protocol Types

The MCP C# SDK provides strongly-typed representations of all Model Context Protocol types defined in the specification.

Namespace

ModelContextProtocol.Protocol

Core Protocol Types

Tool

Represents a tool that the server is capable of calling.

public sealed class Tool : IBaseMetadata

Properties

Name

string

required

The unique identifier for the tool.

Title

string

A human-readable display name for the tool.

Description

string

A human-readable description of the tool that helps AI models understand what the tool does and when to use it.

InputSchema

JsonElement

A JSON Schema object defining the expected parameters for the tool. Must be a valid JSON Schema object with “type” property set to “object”.

OutputSchema

JsonElement

A JSON Schema object defining the expected structured outputs for the tool. Describes the shape of data returned in CallToolResult.StructuredContent.

Annotations

ToolAnnotations

Optional additional tool information and behavior hints, such as whether the tool is read-only, destructive, idempotent, or operates in an open world.

Execution

ToolExecution

Execution-related metadata for this tool, particularly regarding task augmentation support.

Icons

IList<Icon>

An optional list of icons for this tool.

Example

var tool = new Tool
{
    Name = "get_weather",
    Description = "Get current weather for a location",
    InputSchema = JsonSerializer.SerializeToElement(new
    {
        type = "object",
        properties = new
        {
            location = new { type = "string", description = "City name" },
            units = new { type = "string", @enum = new[] { "celsius", "fahrenheit" } }
        },
        required = new[] { "location" }
    })
};

Prompt

Represents a prompt that the server offers.

public sealed class Prompt : IBaseMetadata

Properties

Name

string

required

The unique identifier for the prompt.

Title

string

A human-readable display name for the prompt.

Description

string

An optional description of what this prompt provides.

Arguments

IList<PromptArgument>

A list of arguments that this prompt accepts for templating and customization.

Icons

IList<Icon>

An optional list of icons for this prompt.

Example

var prompt = new Prompt
{
    Name = "code_review",
    Description = "Review code for best practices and potential issues",
    Arguments = new[]
    {
        new PromptArgument
        {
            Name = "language",
            Description = "Programming language",
            Required = true
        },
        new PromptArgument
        {
            Name = "code",
            Description = "Code to review",
            Required = true
        }
    }
};

Resource

Represents a known resource that the server is capable of reading.

public sealed class Resource : IBaseMetadata

Properties

Name

string

required

The unique identifier for the resource.

Title

string

A human-readable display name for the resource.

Uri

string

required

The URI of this resource.

Description

string

A description of what this resource represents.

MimeType

string

The MIME type of this resource (e.g., “text/plain”, “application/json”, “image/png”).

Annotations

Optional annotations specifying the intended audience (User, Assistant, or both) and priority level.

Size

long

The size of the raw resource content (before base64 encoding), in bytes, if known.

Icons

IList<Icon>

An optional list of icons for this resource.

Example

var resource = new Resource
{
    Name = "config",
    Uri = "file:///app/config.json",
    Description = "Application configuration file",
    MimeType = "application/json"
};

ResourceTemplate

Represents a known resource template that the server is capable of reading.

public sealed class ResourceTemplate : IBaseMetadata

Properties

Name

string

required

The unique identifier for the resource template.

UriTemplate

string

required

The URI template (according to RFC 6570) that can be used to construct resource URIs.

Description

string

A description of what this resource template represents.

MimeType

string

The MIME type of resources generated from this template.

IsTemplated

bool

Gets a value that indicates whether UriTemplate contains any template expressions.

Example

var template = new ResourceTemplate
{
    Name = "user_profile",
    UriTemplate = "users://{userId}/profile",
    Description = "User profile data",
    MimeType = "application/json"
};

Content Types

ContentBlock

Base class for different types of content in MCP messages.

Derived Types

TextContentBlock: Plain text content
ImageContentBlock: Base64-encoded image data
AudioContentBlock: Base64-encoded audio data
EmbeddedResourceContentBlock: Reference to an embedded resource

Example

// Text content
var textContent = new TextContentBlock
{
    Text = "Hello, world!"
};

// Image content
var imageContent = new ImageContentBlock
{
    Data = Convert.ToBase64String(imageBytes),
    MimeType = "image/png"
};

PromptMessage

Represents a message within the Model Context Protocol system.

public sealed class PromptMessage

Content

ContentBlock

required

The content of the message, which can be text, image, audio, or an embedded resource.

Role

required

The role of the message sender (User or Assistant).

Example

var message = new PromptMessage
{
    Role = Role.User,
    Content = new TextContentBlock { Text = "What's the weather?" }
};

Result Types

CallToolResult

Represents the result of a tool call request.

public sealed class CallToolResult : Result

Content

IList<ContentBlock>

required

The response content from the tool call.

StructuredContent

JsonElement

An optional JSON object representing the structured result of the tool call.

IsError

bool

Indicates whether the tool call was unsuccessful. When true, the tool execution failed and details are in the Content property.

Task

McpTask

The task data for newly created task (task-augmented tool calls only).

Example - Success

var result = new CallToolResult
{
    Content = new[]
    {
        new TextContentBlock { Text = "Temperature: 22°C" }
    }
};

Example - Error

var result = new CallToolResult
{
    IsError = true,
    Content = new[]
    {
        new TextContentBlock { Text = "Invalid location provided" }
    }
};

GetPromptResult

Represents the result of a prompt retrieval request.

public sealed class GetPromptResult : Result

Messages

IList<PromptMessage>

required

The messages that make up the prompt.

Description

string

An optional description of the prompt.

ReadResourceResult

Represents the result of a resource read request.

public sealed class ReadResourceResult : Result

Contents

IList<ResourceContents>

required

The contents of the resource.

Enumerations

Role

Specifies the role of a message sender.

public enum Role
{
    User,
    Assistant
}

McpErrorCode

Standard MCP error codes.

public enum McpErrorCode
{
    ParseError = -32700,
    InvalidRequest = -32600,
    MethodNotFound = -32601,
    InvalidParams = -32602,
    InternalError = -32603
}

Request and Notification Methods

RequestMethods

Constants for MCP request method names.

public static class RequestMethods
{
    public const string Ping = "ping";
    public const string ToolsList = "tools/list";
    public const string ToolsCall = "tools/call";
    public const string PromptsList = "prompts/list";
    public const string PromptsGet = "prompts/get";
    public const string ResourcesList = "resources/list";
    public const string ResourcesRead = "resources/read";
    public const string ResourcesTemplatesList = "resources/templates/list";
    public const string ResourcesSubscribe = "resources/subscribe";
    public const string ResourcesUnsubscribe = "resources/unsubscribe";
    // ... and more
}

NotificationMethods

Constants for MCP notification method names.

public static class NotificationMethods
{
    public const string Cancelled = "notifications/cancelled";
    public const string Progress = "notifications/progress";
    public const string ResourceUpdatedNotification = "notifications/resources/updated";
    public const string ResourceListChangedNotification = "notifications/resources/list_changed";
    public const string ToolListChangedNotification = "notifications/tools/list_changed";
    public const string PromptListChangedNotification = "notifications/prompts/list_changed";
    // ... and more
}

Core Package

Main Package

ASP.NET Core Package

Namespace

Core Protocol Types

Tool

Properties

Prompt

Properties

Resource

Properties

ResourceTemplate

Properties

Content Types

ContentBlock

Derived Types

PromptMessage

Result Types

CallToolResult

GetPromptResult

ReadResourceResult

Enumerations

Role

McpErrorCode

Request and Notification Methods

RequestMethods

NotificationMethods

See Also

Core Package

Main Package

ASP.NET Core Package

Documentation Index

​Namespace

​Core Protocol Types

​Tool

​Properties

​Prompt

​Properties

​Resource

​Properties

​ResourceTemplate

​Properties

​Content Types

​ContentBlock

​Derived Types

​PromptMessage

​Result Types

​CallToolResult

​GetPromptResult

​ReadResourceResult

​Enumerations

​Role

​McpErrorCode

​Request and Notification Methods

​RequestMethods

​NotificationMethods

​See Also

Namespace

Core Protocol Types

Tool

Properties

Prompt

Properties

Resource

Properties

ResourceTemplate

Properties

Content Types

ContentBlock

Derived Types

PromptMessage

Result Types

CallToolResult

GetPromptResult

ReadResourceResult

Enumerations

Role

McpErrorCode

Request and Notification Methods

RequestMethods

NotificationMethods

See Also