Claude Desktop Extensions release notes / what's new

Anthropic has launched Desktop Extensions, a new packaging format that allows users to install Model Context Protocol (MCP) servers into Claude Desktop with a single click. This update eliminates the requirement for users to install runtimes like Node.js or Python, manually edit JSON configuration files, or resolve dependency conflicts.

Simplified MCP Server Installation

Desktop Extensions transition the installation of local MCP servers from a manual, developer-centric process to a streamlined user experience. Previously, users had to install runtimes, manually edit ~/.claude/claude_desktop_config.json, and manage package versions. With the new .mcpb (MCP Bundle) file extension—which replaces the previous .dxt extension—users can now simply download a bundle and double-click to install it via Claude Desktop.

Technical Architecture of .mcpb Files

A Desktop Extension is a ZIP archive that bundles the MCP server implementation and all its dependencies into a single package. The architecture consists of the following components:

manifest.json: The only required file, containing metadata, configuration, and runtime requirements.
server/: The directory containing the MCP server implementation.
dependencies/: All required packages and libraries (e.g., node_modules for Node.js or lib for Python).
icon.png: An optional icon for the extension.

Claude Desktop simplifies the runtime environment by shipping a built-in Node.js runtime, providing automatic updates for extensions, and storing sensitive API keys in the operating system's keychain.

The Manifest Specification

The manifest.json file defines how the extension operates. Key capabilities include:

Runtime Support: Supports node, python, and binary server types.
User Configuration: Developers can define required inputs (e.g., api_key or allowed_directories). Claude Desktop provides a UI for these inputs, validates them, and stores sensitive values in the OS secret vault.
Dynamic Variables: The manifest supports template literals such as ${__dirname} for the installation directory and ${user_config.key} for user-provided values.
Cross-Platform Overrides: Developers can specify platform-specific commands or environment variables for win32, darwin, and linux.

Developer Toolchain and Workflow

Anthropic provides an open-source toolchain to help developers package existing MCP servers into Desktop Extensions. The workflow involves four primary steps:

Initialization: Running npx @anthropic-ai/mcpb init to generate a manifest.json via an interactive tool.
Configuration: Defining user-required inputs in the user_config section of the manifest.
Packaging: Running npx @anthropic-ai/mcpb pack to validate the manifest and generate the .mcpb archive.
Testing: Dragging the resulting file into the Claude Desktop Settings window for installation.

Ecosystem and Enterprise Security

To foster a broad ecosystem, Anthropic has open-sourced the MCPB specification, packaging tools, and reference implementations. This allows other AI desktop applications to adopt the .mcpb format for consistent extension support.

Enterprise Management

For organizational deployment, Anthropic has introduced several security and administrative controls:

Deployment: Support for Group Policy (Windows) and MDM (macOS) to pre-install approved extensions.
Control: The ability to blocklist specific publishers or extensions and disable the built-in extension directory entirely.
Private Directories: Support for deploying private, organization-specific extension directories.

Capabilities and Use Cases

Desktop Extensions enable Claude to interact with local applications and private data while keeping that data on the user's machine. As a proof of concept, Anthropic demonstrated an extension that connects Claude to the PyBoy GameBoy emulator, allowing the model to take control of the emulator to play games like Super Mario Land.