The phone is the remote
TethrX is a free iPhone and iPad app for Grok Build, a terminal coding agent. The agent, its tools and your code stay on your computer. The phone watches the work stream in, reads the diffs, reviews git, and approves or rejects each tool call, from the app or straight from a notification.
It pairs with a small open source bridge you run yourself and talks to it directly, over Wi-Fi or your own VPN. There is no relay and no server of mine in between, and the App Store privacy label reads Data Not Collected.
Trust that travels in a QR code
A bridge on a laptop has no domain and no certificate authority, so it mints its own certificate, and the pairing QR code carries that certificate's SHA-256 fingerprint. The app accepts exactly that certificate and nothing else, so the very first connection is verified rather than trusted.
The certificate is made to last ten years, on purpose. When a pinned certificate expires nothing warns anyone: every paired phone simply stops connecting, and it looks exactly like a dead bridge.
No dependencies, so I wrote the parts
The bridge has no runtime dependencies at all, which meant writing what a package would have handed me. It signs Apple Push tokens itself with ES256 and speaks HTTP/2 straight to Apple, and it pushes Live Activity updates so the lock screen keeps moving while the app is closed. The pairing token is 192 bits, kept in the Keychain on the phone and compared in constant time on the computer.
Getting past App Review
The first submission was turned down because the app opened on a setup wizard that asked you to install something on a computer. So the app learned to be useful on its own: a welcome screen, a prompt library on the phone, a guided tour. It went live on 10 August 2026, 22 days after the first commit, in eight languages.
Since 1.0
The repository has kept going: an Apple Watch app that never holds a secret (it asks the phone), lock screen widgets, risk labels on commands that destroy data or leave the machine, syntax-highlighted diffs. None of that is in the App Store build yet, and this page will say so until it is.