Best for
- Developers using Cursor, Claude, Visual Studio Code or Windsurf who want to protect their MCP traffic
- Users who want signature-based alerting and blocking at the MCP tool call level
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MCP Defender is a desktop app, acquired by Docker Inc., that proxies MCP tool call requests and responses from AI apps (Cursor, Claude, Visual Studio Code, Windsurf), checks them against signatures, and prompts the user to allow or block when harmful content is detected. It is distributed primarily as a Mac download and can also be run from source. The source material provides no server manifest, tool list, transport, or client config example, so those fields are left empty. It suits developers on these AI clients who want added protection for MCP traffic; it is not for non-Mac users, users expecting config-file installation of an MCP server, or scenarios needing a server-side centralized security gateway.
MCP Defender is a desktop app that protects AI apps like Cursor from a variety of attacks. All MCP tool call requests and responses from AI apps are automatically proxied through MCP Defender; the intercepted data is then checked against a set of signatures. If anything harmful is detected, MCP Defender alerts you and asks whether to allow or block the tool call. It automatically protects Cursor, Claude, Visual Studio Code and Windsurf. MCP Defender has been acquired by Docker Inc.
Setup
- Download MCP Defender for Mac from the GitHub Releases page.
- Alternatively, clone the git repo and run:
npm install
npm start
Fit and risk
Not for
- Users who are not on Mac or do not use the supported AI clients listed above
- Users expecting to install an MCP server via a client config file rather than a desktop app
- Scenarios requiring a server-side or cloud-centralized MCP security gateway (not described in the source)
Required permissions
- Proxying MCP tool call requests and responses between AI apps and MCP servers in order to intercept them
- Inspecting intercepted request and response content locally to match signatures
Risks and side effects
- The source does not describe the signature set or detection coverage, so misses are possible
- All MCP traffic is proxied through the desktop app, so proxy issues could affect normal tool calls in AI apps
- Allow-or-block decisions on suspected harmful content depend on the user, and false positives may block legitimate calls
- The source does not describe how data is processed or stored, so privacy impact should be assessed independently
Troubleshooting
- Make sure the latest version is downloaded and installed from GitHub Releases
- If running from source fails, run npm install before npm start
- Confirm the AI app in use is one of the supported ones: Cursor, Claude, Visual Studio Code or Windsurf
- If a tool call is blocked, review the MCP Defender alert and choose to allow or block
- Confirm the app is being proxied by MCP Defender so its MCP tool call requests and responses are intercepted
Use cases
Automatically proxy and inspect MCP tool calls while using Cursor, Claude, VS Code or Windsurf
Get alerted and choose to allow or block when a harmful MCP tool call request or response is detected
Add a layer of security to MCP traffic while developing AI apps locally