Mac Bridge

Let an AI securely drive a macOS machine, from anywhere.

An MCP server that runs on a Mac and exposes a small, sharp set of tools (shell, file transfer, binary execution, screenshots) over a token-protected network port. Point your AI client at it and it can build, test, and automate on macOS, even when your AI is running on Windows or Linux.

   your machine (Windows / Linux / Mac)            the Mac you want to control
 ┌────────────────────────────────────┐           ┌────────────────────────────┐
 │  AI client (MCP host)              │  HTTP +   │      mac-bridge-mcp        │
 │  e.g. Claude Desktop, an agent     │ ───────►  │  ┌──────────────────────┐  │
 │                                    │  bearer   │  │ IP allowlist → token │  │
 │  "build & test my binary on macOS" │  token    │  └──────────┬───────────┘  │
 │                                    │ ◄───────  │     shell · files · exec   │
 └────────────────────────────────────┘  results  └────────────────────────────┘

⚠️ Warning - this is remote code execution on the host Mac, by design. Anyone who can reach the port and has the token gets the equivalent of a shell. Run it only on machines you own, keep the port off the public internet, and read the Security model before exposing it anywhere. The token is as sensitive as an SSH key.

Table of contents

• Why
• Features
• Quickstart
• Installation
• Configuration
• Connecting your AI client
• Tools
• Example: cross-platform binary test loop
• Security model
• macOS permissions
• License

Why

If you ship software that has to run on both Windows and macOS, you constantly need "the other OS" in the loop, to compile a native binary, run the test suite, reproduce a platform-specific bug, or grab a screenshot of how something renders. mac-bridge-mcp puts a Mac one tool-call away from whatever AI you're already working with, so a single conversation can drive both platforms.

The original motivation was cross-platform security research. When an AI reviews source code that compiles on Windows, Linux, and macOS, it will sometimes surface a vulnerability that only manifests on macOS, and then have no way to confirm it. Lacking access to a macOS system, it can't compile the affected code, run a proof-of-concept, and check whether the finding is genuine or a false positive. mac-bridge-mcp closes that gap: it gives the AI a real Mac to compile, test, and verify on, so macOS-specific findings can be triaged on the actual operating system instead of guessed at.

It speaks MCP's Streamable HTTP transport, so any MCP-capable client can use it, locally or across the network.

Features

• Real macOS control - shell commands, direct binary execution, file read/write, directory listing, and screen capture.
• Two security gates - an optional source-IP allowlist (with CIDR support) in front of a constant-time bearer-token check.
• Built-in TLS - serve HTTPS directly from a cert + key, or rely on an SSH tunnel / VPN. No reverse proxy required.
• Optional filesystem jail - confine every operation under one directory.
• Works across machines - drive a Mac from Windows or Linux over an SSH tunnel or a private VPN.
• Tiny and readable - one dependency-light Python module, easy to audit and extend.
• Client-agnostic - works with any MCP host, with a drop-in mcp-remote config for stdio-only clients.

Quickstart

On the Mac (the machine you want to control):

# 1. Get the code and install the two dependencies
git clone https://github.com/YOUR_USERNAME/mac-bridge-mcp
cd mac-bridge-mcp
pip install fastmcp uvicorn        # or: pip install -r requirements.txt

# 2. Generate a token and run the server
export MCP_BRIDGE_TOKEN="$(python3 -c 'import secrets;print(secrets.token_urlsafe(32))')"
echo "Token: $MCP_BRIDGE_TOKEN"    # copy this
python3 src/mac_bridge_mcp/server.py

With the default MCP_BRIDGE_HOST=127.0.0.1, the server is reachable only from the Mac itself. To connect from another machine, open an SSH tunnel and point your client at the local end of it:

ssh -L 8765:127.0.0.1:8765 you@your-mac     # then connect to http://127.0.0.1:8765/mcp

If you bind to an address your other machine can already reach, for example the Mac's Tailscale or LAN IP via MCP_BRIDGE_HOST, you don't need the tunnel. Just connect straight to http://<that-ip>:8765/mcp. In that case encrypt the connection by enabling TLS / HTTPS (or keep it on a trusted private network/VPN), and never bind to a public address (see the Security model).

Installation

From source:

git clone https://github.com/YOUR_USERNAME/mac-bridge-mcp
cd mac-bridge-mcp
pip install -e .

Requires Python 3.10+ on macOS.

Configuration

Everything is configured through environment variables (or a local .env, see .env.example).

Variable	Default	Purpose
MCP_BRIDGE_TOKEN	random	Shared secret ("password"). Set it to keep it stable across restarts.
MCP_BRIDGE_HOST	127.0.0.1	Bind address. Do not use 0.0.0.0 on an untrusted network.
MCP_BRIDGE_PORT	8765	Listen port.
MCP_BRIDGE_PATH	/mcp	URL path for the MCP endpoint.
MCP_BRIDGE_SHELL	/bin/zsh	Shell used by run_command.
MCP_BRIDGE_ALLOW_IPS	unset	Comma-separated IPs/CIDRs allowed to connect. Unset = any IP (token still required).
MCP_BRIDGE_ROOT	unset	Confine all file/binary operations under this directory.
MCP_BRIDGE_TLS_CERT	unset	Path to a PEM certificate. Set with MCP_BRIDGE_TLS_KEY to serve HTTPS.
MCP_BRIDGE_TLS_KEY	unset	Path to the certificate's private key (PEM).
MCP_BRIDGE_TLS_KEY_PASSWORD	unset	Password for the private key, if it is encrypted.
MCP_BRIDGE_TRUST_FORWARDED	unset	Read client IP from X-Forwarded-For. ONLY behind a proxy you control.

Connecting your AI client

The server and your AI usually run on different machines. Two cases:

Your client supports remote / HTTP MCP servers directly - point it at http://<host>:8765/mcp and add the header Authorization: Bearer <token>.

Your client only launches local stdio servers (the classic Claude Desktop pattern), use the mcp-remote bridge, which runs locally and forwards to the remote server. See examples/claude_desktop_config.json:

{
  "mcpServers": {
    "mac-bridge": {
      "command": "npx",
      "args": [
        "mcp-remote",
        "http://MAC_IP_OR_HOST:8765/mcp",
        "--header", "Authorization: Bearer YOUR_TOKEN_HERE"
      ]
    }
  }
}

Test before wiring up an AI with the MCP Inspector (no model required):

npx @modelcontextprotocol/inspector
# URL: http://127.0.0.1:8765/mcp   (transport: Streamable HTTP)
# Header: Authorization: Bearer <token>

...or run the included smoke test:

TOKEN=your-token ./examples/smoke_test.sh

Tools

Tool	Description
system_info	macOS version, CPU architecture (arm64 / x86_64), hostname, user. Call first.
run_command	Run a shell command; returns stdout, stderr, exit code, timeout flag.
run_binary	Execute a binary directly with verbatim args (no shell parsing).
list_dir	List a directory with type, size, and mode for each entry.
read_file	Read a file as text, or base64 for binaries.
write_file	Write a file; base64_encoded + make_executable for pushing binaries.
screenshot	Capture the screen as a base64 PNG (needs Screen Recording permission).

Every tool returns a structured result and handles its own errors, so the AI gets a clean signal instead of a stack trace.

Example: cross-platform binary test loop

A typical "I built it on Windows, does it work on macOS?" round-trip:

1. system_info - confirm arch is arm64 vs x86_64.
2. write_file - push your built artifact (base64, make_executable=true).
3. run_binary - run it with test arguments; inspect stdout / exit_code.
4. read_file - pull back any output files it produced.

Because the AI sees the architecture first, it can pick the right build and even recompile via run_command (clang, cargo build, go build, ...) before testing.

🔐 Security model

Requests pass through two gates, in order, on every request:

1. IP allowlist (MCP_BRIDGE_ALLOW_IPS) - a peer outside the list is rejected with 403 before the token is even compared. Supports single addresses and CIDR ranges, IPv4 and IPv6.
2. Bearer token - checked with a constant-time comparison; missing/wrong gives 401.

An optional filesystem jail (MCP_BRIDGE_ROOT) then confines every path argument to a chosen directory.

What IP does the server actually see?

• SSH tunnel - traffic arrives from 127.0.0.1 (the tunnel exit on the Mac), so include 127.0.0.1/::1 in the allowlist; your real gate there is the SSH login itself.

• Tailscale / WireGuard / LAN - the server sees the client's real address, so the allowlist is meaningful. Pin it to your client's VPN IP or LAN subnet:

  export MCP_BRIDGE_ALLOW_IPS="127.0.0.1,::1,100.64.0.0/10,192.168.1.0/24"
  

Operating rules of thumb

• Keep MCP_BRIDGE_HOST=127.0.0.1; reach the server via SSH tunnel or a private VPN. Never put it on the public internet.
• Use a long random token; rotate it if it leaks; never commit .env.
• Run as a normal user, not root.
• Encrypt the connection. The server can serve HTTPS itself (see TLS / HTTPS), or you can rely on an SSH tunnel / VPN for encryption. Don't send the token over plain HTTP across a network. Leave MCP_BRIDGE_TRUST_FORWARDED off unless a reverse proxy you control sets it.

TLS / HTTPS

The server has built-in TLS, point it at a certificate and key and it serves https:// directly, no reverse proxy required:

export MCP_BRIDGE_TLS_CERT="/path/to/server.crt"
export MCP_BRIDGE_TLS_KEY="/path/to/server.key"
python3 src/mac_bridge_mcp/server.py        # now on https://...

Three easy ways to get a certificate, best first:

• Tailscale (recommended): if you reach the Mac over Tailscale, run tailscale cert <machine>.<tailnet>.ts.net. You get a real, trusted certificate with no client-side configuration, clients verify it normally.

• mkcert (LAN): mkcert installs a local CA and issues certs your machines trust. Good for a home/office LAN.

• Self-signed: run examples/gen_self_signed_cert.sh. The traffic is encrypted, but clients don't trust a self-signed cert by default and will refuse to connect until told to trust it. For the mcp-remote bridge that means pointing Node at your cert:

  NODE_EXTRA_CA_CERTS=/path/to/server.crt npx mcp-remote https://<host>:8765/mcp \
    --header "Authorization: Bearer <token>"
  

When TLS is on, use https:// in every client URL. The MCP_BRIDGE_ALLOW_IPS and token gates apply exactly the same over HTTPS.

macOS permissions

• Shell and file tools need no special permission.
• screenshot needs Screen Recording for whatever process runs the server (Terminal / iTerm / python): System Settings -> Privacy & Security -> Screen Recording, then restart that app.
• Future mouse/keyboard control will need Accessibility permission in the same place.

License

MIT © IamLeandrooooo

---

Built on the Model Context Protocol and FastMCP.