MCP Desktop Extensions (.mcpb) Explained: One-Click Local MCP Servers

An MCP desktop extension is a local MCP server packed into a single .mcpb file that you install with one click, like a browser extension. The file is a zip archive holding the server, its dependencies and a manifest.json that tells Claude Desktop how to run it and what settings it needs. You no longer edit a JSON config file or install Node.js yourself.

The format started life as Desktop Extensions (.dxt) and is now called MCP Bundles (.mcpb). This guide explains what they are, how installation and settings work, what admins can control, and what changed in Anthropic's directory in 2026. Sources were checked on 2 November 2026.

The problem desktop extensions solve

Before extensions, adding a local MCP server meant editing claude_desktop_config.json, installing the right runtime, and pasting API keys into a text file. Our guide to the Claude Desktop config file location shows that older route, which still works.

Anthropic's Desktop Extensions post (26 June 2025) describes the fix: "bundling an entire MCP server" with its dependencies into one file. Users download it, open it in Claude Desktop and click Install, "with no terminal or manual config edits."

What is inside a .mcpb file

The MCPB repository, now under the Model Context Protocol GitHub organization, says "MCP Bundles (.mcpb) are zip archives containing a local MCP server and a manifest.json." It adds: "A manifest.json is the only required file."

The manifest spec covers:

• Identity: name, version, description and author.
• Server: a type of node, python, binary or uv, an entry point, and the command to run.
• User settings: a user_config block for things like API keys or allowed folders, with types such as string, number, boolean, directory and file. A sensitive flag masks secrets.
• Compatibility: which Claude Desktop versions, operating systems (darwin, win32, linux) and runtimes the extension needs.
• Tools and prompts: a declared list, so users can see what the extension does before installing.

The extension talks to Claude over the stdio transport, the local transport in the MCP spec.

How installation works

Anthropic's MCPB build guide lists three ways to install:

• Double-click the .mcpb file.
• Drag it into the Claude Desktop window.
• Go to Settings > Extensions > Advanced settings > Install Extension… and pick the file.

Each opens an install screen where you review the extension's details and permissions and fill in required settings. Installation is per user.

The Claude help center article on local MCP servers adds that "Claude Desktop includes a built-in Node.js environment, so Node.js installation isn't required." It also says extensions from the official directory "update automatically by default," while privately shared ones need a manual reinstall to update.

Where your secrets go

When an extension needs an API key, Claude Desktop shows a settings form generated from the manifest. Anthropic's post says "Sensitive configuration like API keys are stored in the OS keychain." The help center names Keychain on macOS and Credential Manager on Windows. That is safer than a plain-text config file.

Controls for companies

Local servers run on staff laptops, so admins need a say. The help center says "Owners and Primary Owners of Team and Enterprise plans can manage team access to desktop extensions," including turning public extensions on or off and uploading custom ones. There is also an allowlist feature, and "Enterprise policy controls at the user-machine level will override any in-app controls."

Anthropic's original post lists Group Policy on Windows and MDM on macOS, pre-installing approved extensions, blocking extensions or publishers, and private directories. Our playbook on an approved server list shows how to decide what goes on it.

The 2026 directory change

This is the change most older guides miss. Anthropic's build guide now says: "Desktop extension listings in the directory are deprecated, and the directory no longer accepts MCPB submissions. To distribute a local MCP server through the directory, include it in a plugin."

So in November 2026:

• You can still build and share .mcpb files privately, for example on your website or inside your company.
• Users can still install them by double-click or from Settings.
• New public listings of local servers go through Claude's plugin submission, not as standalone extensions.

MCPB or a remote connector?

Anthropic's build guide compares the two. Choose MCPB when you need access to systems behind a firewall, direct file access, locally installed tools, or data that should not leave the machine. Choose a remote connector for cloud services, OAuth with server-side tokens, and reach across Claude on web, mobile and desktop. Our lesson on remote vs local servers goes deeper.

Risks to keep in mind

An extension is code that runs on your computer with your user's permissions. One click makes installing easy, which also makes installing something bad easy.

• Install only from publishers you trust.
• Read the declared tools and requested folders before you click Install.
• Prefer signed bundles. The MCPB CLI includes mcpb verify, which reports the signature and warns if a certificate is self-signed.
• Use the MCP server risk checklist before approving one for your team.

See sandboxing local MCP servers for ways to limit damage.

Next step

If you want to package your own server, follow our tutorial on how to build a Claude desktop extension. If you need a local connector for internal systems built and signed for your team, our MCP development team can help.

Frequently asked questions