Mcp Connector ↗

Claude’s Model Context Protocol (MCP) connector feature enables you to connect to remote MCP servers directly from the Messages API without a separate MCP client.

Current version: This feature requires the beta header: "anthropic-beta": "mcp-client-2025-11-20"

The previous version (mcp-client-2025-04-04) is deprecated. See the deprecated version documentation below.

This feature is in beta and is not covered by Zero Data Retention (ZDR) arrangements. Beta features are excluded from ZDR.

Key features#

• Direct API integration: Connect to MCP servers without implementing an MCP client
• Tool calling support: Access MCP tools through the Messages API
• Flexible tool configuration: Enable all tools, allowlist specific tools, or denylist unwanted tools
• Per-tool configuration: Configure individual tools with custom settings
• OAuth authentication: Support for OAuth Bearer tokens for authenticated servers
• Multiple servers: Connect to multiple MCP servers in a single request

Limitations#

• Of the feature set of the MCP specification, only tool calls are currently supported.
• The server must be publicly exposed through HTTP (supports both Streamable HTTP and SSE transports). Local STDIO servers cannot be connected directly.
• The MCP connector is currently not supported on Amazon Bedrock and Google Vertex.

Using the MCP connector in the Messages API#

The MCP connector uses two components:

1. MCP Server Definition (mcp_servers array): Defines server connection details (URL, authentication)
2. MCP Toolset (tools array): Configures which tools to enable and how to configure them

Basic example#

This example enables all tools from an MCP server with default configuration:

curl https://api.anthropic.com/v1/messages \
  -H "Content-Type: application/json" \
  -H "X-API-Key: $ANTHROPIC_API_KEY" \
  -H "anthropic-version: 2023-06-01" \
  -H "anthropic-beta: mcp-client-2025-11-20" \
  -d '{
    "model": "claude-opus-4-6",
    "max_tokens": 1000,
    "messages": [{"role": "user", "content": "What tools do you have available?"}],
    "mcp_servers": [
      {
        "type": "url",
        "url": "https://example-server.modelcontextprotocol.io/sse",
        "name": "example-mcp",
        "authorization_token": "YOUR_TOKEN"
      }
    ],
    "tools": [
      {
        "type": "mcp_toolset",
        "mcp_server_name": "example-mcp"
      }
    ]
  }'

const anthropic = new Anthropic();

const response = await anthropic.beta.messages.create({
  model: "claude-opus-4-6",
  max_tokens: 1000,
  messages: [
    {
      role: "user",
      content: "What tools do you have available?"
    }
  ],
  mcp_servers: [
    {
      type: "url",
      url: "https://example-server.modelcontextprotocol.io/sse",
      name: "example-mcp",
      authorization_token: "YOUR_TOKEN"
    }
  ],
  tools: [
    {
      type: "mcp_toolset",
      mcp_server_name: "example-mcp"
    }
  ],
  betas: ["mcp-client-2025-11-20"]
});

import anthropic

client = anthropic.Anthropic()

response = client.beta.messages.create(
    model="claude-opus-4-6",
    max_tokens=1000,
    messages=[{"role": "user", "content": "What tools do you have available?"}],
    mcp_servers=[
        {
            "type": "url",
            "url": "https://mcp.example.com/sse",
            "name": "example-mcp",
            "authorization_token": "YOUR_TOKEN",
        }
    ],
    tools=[{"type": "mcp_toolset", "mcp_server_name": "example-mcp"}],
    betas=["mcp-client-2025-11-20"],
)

MCP server configuration#

Each MCP server in the mcp_servers array defines the connection details:

{
  "type": "url",
  "url": "https://example-server.modelcontextprotocol.io/sse",
  "name": "example-mcp",
  "authorization_token": "YOUR_TOKEN"
}

Field descriptions#

MCP toolset configuration#

The MCPToolset lives in the tools array and configures which tools from the MCP server are enabled and how they should be configured.

Basic structure#

{
  "type": "mcp_toolset",
  "mcp_server_name": "example-mcp",
  "default_config": {
    "enabled": true,
    "defer_loading": false
  },
  "configs": {
    "specific_tool_name": {
      "enabled": true,
      "defer_loading": true
    }
  }
}

Field descriptions#

Tool configuration options#

Each tool (whether configured in default_config or in configs) supports the following fields:

Configuration merging#

Configuration values merge with this precedence (highest to lowest):

1. Tool-specific settings in configs
2. Set-level default_config
3. System defaults

Example:

{
  "type": "mcp_toolset",
  "mcp_server_name": "google-calendar-mcp",
  "default_config": {
    "defer_loading": true
  },
  "configs": {
    "search_events": {
      "enabled": false
    }
  }
}

Results in:

• search_events: enabled: false (from configs), defer_loading: true (from default_config)
• All other tools: enabled: true (system default), defer_loading: true (from default_config)

Common configuration patterns#

Enable all tools with default configuration#

The simplest pattern - enable all tools from a server:

{
  "type": "mcp_toolset",
  "mcp_server_name": "google-calendar-mcp"
}

Allowlist - Enable only specific tools#

Set enabled: false as the default, then explicitly enable specific tools:

{
  "type": "mcp_toolset",
  "mcp_server_name": "google-calendar-mcp",
  "default_config": {
    "enabled": false
  },
  "configs": {
    "search_events": {
      "enabled": true
    },
    "create_event": {
      "enabled": true
    }
  }
}

Denylist - Disable specific tools#

Enable all tools by default, then explicitly disable unwanted tools:

{
  "type": "mcp_toolset",
  "mcp_server_name": "google-calendar-mcp",
  "configs": {
    "delete_all_events": {
      "enabled": false
    },
    "share_calendar_publicly": {
      "enabled": false
    }
  }
}

Mixed - Allowlist with per-tool configuration#

Combine allowlisting with custom configuration for each tool:

{
  "type": "mcp_toolset",
  "mcp_server_name": "google-calendar-mcp",
  "default_config": {
    "enabled": false,
    "defer_loading": true
  },
  "configs": {
    "search_events": {
      "enabled": true,
      "defer_loading": false
    },
    "list_events": {
      "enabled": true
    }
  }
}

In this example:

• search_events is enabled with defer_loading: false
• list_events is enabled with defer_loading: true (inherited from default_config)
• All other tools are disabled

Validation rules#

The API enforces these validation rules:

• Server must exist: The mcp_server_name in an MCPToolset must match a server defined in the mcp_servers array
• Server must be used: Every MCP server defined in mcp_servers must be referenced by exactly one MCPToolset
• Unique toolset per server: Each MCP server can only be referenced by one MCPToolset
• Unknown tool names: If a tool name in configs doesn’t exist on the MCP server, a backend warning is logged but no error is returned (MCP servers may have dynamic tool availability)

Response content types#

When Claude uses MCP tools, the response will include two new content block types:

MCP Tool Use Block#

{
  "type": "mcp_tool_use",
  "id": "mcptoolu_014Q35RayjACSWkSj4X2yov1",
  "name": "echo",
  "server_name": "example-mcp",
  "input": { "param1": "value1", "param2": "value2" }
}

MCP Tool Result Block#

{
  "type": "mcp_tool_result",
  "tool_use_id": "mcptoolu_014Q35RayjACSWkSj4X2yov1",
  "is_error": false,
  "content": [
    {
      "type": "text",
      "text": "Hello"
    }
  ]
}

Multiple MCP servers#

You can connect to multiple MCP servers by including multiple server definitions in mcp_servers and a corresponding MCPToolset for each in the tools array:

{
  "model": "claude-opus-4-6",
  "max_tokens": 1000,
  "messages": [
    {
      "role": "user",
      "content": "Use tools from both mcp-server-1 and mcp-server-2 to complete this task"
    }
  ],
  "mcp_servers": [
    {
      "type": "url",
      "url": "https://mcp.example1.com/sse",
      "name": "mcp-server-1",
      "authorization_token": "TOKEN1"
    },
    {
      "type": "url",
      "url": "https://mcp.example2.com/sse",
      "name": "mcp-server-2",
      "authorization_token": "TOKEN2"
    }
  ],
  "tools": [
    {
      "type": "mcp_toolset",
      "mcp_server_name": "mcp-server-1"
    },
    {
      "type": "mcp_toolset",
      "mcp_server_name": "mcp-server-2",
      "default_config": {
        "defer_loading": true
      }
    }
  ]
}

Authentication#

For MCP servers that require OAuth authentication, you’ll need to obtain an access token. The MCP connector beta supports passing an authorization_token parameter in the MCP server definition. API consumers are expected to handle the OAuth flow and obtain the access token prior to making the API call, as well as refreshing the token as needed.

Obtaining an access token for testing#

The MCP inspector can guide you through the process of obtaining an access token for testing purposes.

1. Run the inspector with the following command. You need Node.js installed on your machine.

   npx @modelcontextprotocol/inspector

2. In the sidebar on the left, for “Transport type”, select either “SSE” or “Streamable HTTP”.

3. Enter the URL of the MCP server.

4. In the right area, click on the “Open Auth Settings” button after “Need to configure authentication?”.

5. Click “Quick OAuth Flow” and authorize on the OAuth screen.

6. Follow the steps in the “OAuth Flow Progress” section of the inspector and click “Continue” until you reach “Authentication complete”.

7. Copy the access_token value.

8. Paste it into the authorization_token field in your MCP server configuration.

Using the access token#

Once you’ve obtained an access token using either OAuth flow above, you can use it in your MCP server configuration:

{
  "mcp_servers": [
    {
      "type": "url",
      "url": "https://example-server.modelcontextprotocol.io/sse",
      "name": "authenticated-server",
      "authorization_token": "YOUR_ACCESS_TOKEN_HERE"
    }
  ]
}

For detailed explanations of the OAuth flow, refer to the Authorization section in the MCP specification.

Client-side MCP helpers (TypeScript)#

If you manage your own MCP client connection (for example, with local stdio servers, MCP prompts, or MCP resources), the TypeScript SDK provides helper functions that convert between MCP types and Claude API types. This eliminates manual conversion code when using the MCP SDK alongside the Anthropic SDK.

These helpers are currently available in the TypeScript SDK only. Use the mcp_servers API parameter when you have remote servers accessible via URL and only need tool support. If you’re using the Agent SDK, MCP connections are managed automatically. Use the client-side helpers when you need local servers, prompts, resources, or more control over the connection with the base SDK.

Installation#

Install both the Anthropic SDK and the MCP SDK:

npm install @anthropic-ai/sdk @modelcontextprotocol/sdk

Available helpers#

Import the helpers from the beta namespace:

Use MCP tools#

Convert MCP tools for use with the SDK’s tool runner, which handles tool execution automatically:

const anthropic = new Anthropic();

// Connect to an MCP server
const transport = new StdioClientTransport({ command: "mcp-server", args: [] });
const mcpClient = new Client({ name: "my-client", version: "1.0.0" });
await mcpClient.connect(transport);

// List tools and convert them for the Claude API
const { tools } = await mcpClient.listTools();
const runner = await anthropic.beta.messages.toolRunner({
  model: "claude-sonnet-4-6",
  max_tokens: 1024,
  messages: [{ role: "user", content: "What tools do you have available?" }],
  tools: mcpTools(tools, mcpClient)
});

Use MCP prompts#

Convert MCP prompt messages into Claude API message format:

const { messages } = await mcpClient.getPrompt({ name: "my-prompt" });
const response = await anthropic.beta.messages.create({
  model: "claude-sonnet-4-6",
  max_tokens: 1024,
  messages: mcpMessages(messages)
});

Use MCP resources#

Convert MCP resources into content blocks to include in messages, or into file objects for upload:

// As a content block in a message
const resource = await mcpClient.readResource({ uri: "file:///path/to/doc.txt" });
await anthropic.beta.messages.create({
  model: "claude-sonnet-4-6",
  max_tokens: 1024,
  messages: [
    {
      role: "user",
      content: [
        mcpResourceToContent(resource),
        { type: "text", text: "Summarize this document" }
      ]
    }
  ]
});

// As a file upload
const fileResource = await mcpClient.readResource({ uri: "file:///path/to/data.json" });
await anthropic.beta.files.upload({ file: mcpResourceToFile(fileResource) });

Error handling#

The conversion functions throw UnsupportedMCPValueError if an MCP value isn’t supported by the Claude API. This can happen with unsupported content types, MIME types, or non-HTTP resource links.

Migration guide#

If you’re using the deprecated mcp-client-2025-04-04 beta header, follow this guide to migrate to the new version.

Key changes#

1. New beta header: Change from mcp-client-2025-04-04 to mcp-client-2025-11-20
2. Tool configuration moved: Tool configuration now lives in the tools array as MCPToolset objects, not in the MCP server definition
3. More flexible configuration: New pattern supports allowlisting, denylisting, and per-tool configuration

Migration steps#

Before (deprecated):

{
  "model": "claude-opus-4-6",
  "max_tokens": 1000,
  "messages": [
    // ...
  ],
  "mcp_servers": [
    {
      "type": "url",
      "url": "https://mcp.example.com/sse",
      "name": "example-mcp",
      "authorization_token": "YOUR_TOKEN",
      "tool_configuration": {
        "enabled": true,
        "allowed_tools": ["tool1", "tool2"]
      }
    }
  ]
}

After (current):

{
  "model": "claude-opus-4-6",
  "max_tokens": 1000,
  "messages": [
    // ...
  ],
  "mcp_servers": [
    {
      "type": "url",
      "url": "https://mcp.example.com/sse",
      "name": "example-mcp",
      "authorization_token": "YOUR_TOKEN"
    }
  ],
  "tools": [
    {
      "type": "mcp_toolset",
      "mcp_server_name": "example-mcp",
      "default_config": {
        "enabled": false
      },
      "configs": {
        "tool1": {
          "enabled": true
        },
        "tool2": {
          "enabled": true
        }
      }
    }
  ]
}

Common migration patterns#

Deprecated version: mcp-client-2025-04-04#

This version is deprecated. Please migrate to mcp-client-2025-11-20 using the migration guide above.

The previous version of the MCP connector included tool configuration directly in the MCP server definition:

{
  "mcp_servers": [
    {
      "type": "url",
      "url": "https://example-server.modelcontextprotocol.io/sse",
      "name": "example-mcp",
      "authorization_token": "YOUR_TOKEN",
      "tool_configuration": {
        "enabled": true,
        "allowed_tools": ["example_tool_1", "example_tool_2"]
      }
    }
  ]
}

Deprecated field descriptions#