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MCP connector

  • URL: https://platform.claude.com/docs/en/agents-and-tools/mcp-connector.md
  • Retrieved: 2026-01-08T05:11:28.732847+00:00

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.

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:

```bash Shell 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-sonnet-4-5", "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" } ] }'

```typescript TypeScript
import { Anthropic } from '@anthropic-ai/sdk';

const anthropic = new Anthropic();

const response = await anthropic.beta.messages.create({
  model: "claude-sonnet-4-5",
  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"],
});

```python Python import anthropic

client = anthropic.Anthropic()

response = client.beta.messages.create( model="claude-sonnet-4-5", 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"] )

</CodeGroup>

## MCP server configuration

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

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

Field descriptions

Property Type Required Description
type string Yes Currently only "url" is supported
url string Yes The URL of the MCP server. Must start with https://
name string Yes A unique identifier for this MCP server. Must be referenced by exactly one MCPToolset in the tools array.
authorization_token string No OAuth authorization token if required by the MCP server. See MCP specification.

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

Property Type Required Description
type string Yes Must be "mcp_toolset"
mcp_server_name string Yes Must match a server name defined in the mcp_servers array
default_config object No Default configuration applied to all tools in this set. Individual tool configs in configs will override these defaults.
configs object No Per-tool configuration overrides. Keys are tool names, values are configuration objects.
cache_control object No Cache breakpoint configuration for this toolset

Tool configuration options

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

Property Type Default Description
enabled boolean true Whether this tool is enabled
defer_loading boolean false If true, tool description is not sent to the model initially. Used with Tool Search Tool.

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-sonnet-4-5",
  "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.

bash npx @modelcontextprotocol/inspector

  1. In the sidebar on the left, for "Transport type", select either "SSE" or "Streamable HTTP".
  2. Enter the URL of the MCP server.
  3. In the right area, click on the "Open Auth Settings" button after "Need to configure authentication?".
  4. Click "Quick OAuth Flow" and authorize on the OAuth screen.
  5. Follow the steps in the "OAuth Flow Progress" section of the inspector and click "Continue" until you reach "Authentication complete".
  6. Copy the access_token value.
  7. 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.

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-sonnet-4-5",
  "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-sonnet-4-5",
  "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

Old pattern New pattern
No tool_configuration (all tools enabled) MCPToolset with no default_config or configs
tool_configuration.enabled: false MCPToolset with default_config.enabled: false
tool_configuration.allowed_tools: [...] MCPToolset with default_config.enabled: false and specific tools enabled in configs

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

Property Type Description
tool_configuration object Deprecated: Use MCPToolset in the tools array instead
tool_configuration.enabled boolean Deprecated: Use default_config.enabled in MCPToolset
tool_configuration.allowed_tools array Deprecated: Use allowlist pattern with configs in MCPToolset