Two AI agents.
One feature.
A contract they can't talk their way out of.

The mental model in one line: ngrok is a small separate program the host runs that creates a public web address and quietly forwards it to their own localhost:8787 (8787 is the default MCP port — the host can run the broker on any port; just point ngrok at that one). When your buddy is on another machine, this is what makes the broker reachable.

1. 1
   Host starts ngrok in a terminal

   Separate from the app. This tells ngrok: give me a public https URL and forward anything that hits it to my local port 8787.

   ngrok http 8787
   
   Forwarding  https://abc-123.ngrok-free.app  ->  http://localhost:8787

2. 2
   A public doorway now exists

   That https://abc-123.ngrok-free.app leads straight to the host's machine on port 8787. Nothing is listening yet — the broker isn't up — so hitting it now would 502. That's fine; the broker starts next.
3. 3
   Paste the URL, start the broker

   In the app, fill the form and paste that URL into the Public URL field. Leave "Private network" OFF — ngrok is a public tunnel, not a VPN — then click Create & start broker. The chain goes live: ngrok URL → ngrok → localhost:8787.
4. 4
   Why paste the URL at all?

   So the invite links embed it. Without it, links would point at http://127.0.0.1:8787 — which only means "this same machine," useless to a remote buddy. Pasting the ngrok URL makes every link say "reach the broker at https://abc-123.ngrok-free.app."
5. 5
   Share the link, buddy joins

   The sb1_… link now carries the ngrok URL as the broker address. When the buddy joins, they get a command wiring their Claude to the tunnel:

   claude mcp add --transport http sys-buddy \
     https://abc-123.ngrok-free.app/mcp \
     --header "Authorization: Bearer <token>"

6. 6
   Connected

   Every call the buddy's Claude makes now flows through the tunnel to the host's broker — the full path is below.

The one big difference from ngrok: both of you install Tailscale. ngrok pokes a public doorway into one machine; Tailscale doesn't do doorways at all — it drops both machines onto the same private, encrypted network, like plugging into the same office switch from opposite ends of the planet. Nothing ever touches the public internet.

1. 1
   Both of you install Tailscale and log in

   The one step ngrok doesn't need. Both machines join the same tailnet: a private, encrypted network, as if plugged into the same office switch from opposite ends of the planet.
2. 2
   Host runs tailscale serve

   This publishes the broker on your tailnet at an https …ts.net address with a real TLS certificate — no raw IPs, no plain http.

   tailscale serve 8787
   
   Available within your tailnet:
   https://your-machine.tailnet.ts.net/

3. 3
   Paste the ts.net URL, start the broker

   In the app choose Private network, paste https://your-machine.tailnet.ts.net, then Create & start broker. Nothing is ever exposed to the public internet.
4. 4
   Why paste the URL?

   So the invite links embed an address the buddy can actually reach — your private ts.net URL instead of localhost, which only means "this same machine."
5. 5
   Share the invite link

   The buddy's link now points at https://your-machine.tailnet.ts.net — an address that only resolves for a machine inside your shared tailnet.
6. 6
   Buddy joins and runs the command

   Same shape as ngrok — an https address either way:

   claude mcp add --transport http sys-buddy \
     https://your-machine.tailnet.ts.net/mcp \
     --header "Authorization: Bearer <token>"

7. 7
   Connected — privately

   Every call rides the WireGuard-encrypted tailnet straight to the broker. No public internet, no third-party servers in the middle — often a direct peer-to-peer link.