# Gearslip Bring any app to your car screen. ## What Gearslip is Gearslip is an Android Auto client for the phone. It speaks the Android Auto protocol directly to a car head unit over USB, with no Google software in the path. Gearslip acts as a Car App Library host: an app that ships a car interface hands Gearslip a template, and Gearslip renders that template natively on the car screen. Nothing is mirrored from the phone. For apps without a car interface, Gearslip offers a separate screen-sharing mode. The author reverse-engineered the protocol for interoperability, so that a client other than Google's own can talk to a car head unit. ## Status - **Templated apps work.** Gearslip renders all 16 template types that the Car App Library defines, and it draws its own keyboard for search and sign-in. It has been tested against several real navigation and media apps. - **Media playback works.** Gearslip lets you browse and control car-enabled media apps from the car screen, with lyrics and playback state, over the same host connection. - **Audio reaches the car by capturing playback, not by mirroring the screen.** Android requires a screen-share style consent dialog and indicator for this, even though Gearslip never reads the screen; that grant is the only way a non-privileged app can tap another app's audio. The consent normally repeats every drive; the app's own setup steps include two optional adb commands that reduce it to a one-time grant. - **A real head unit needs a certificate that Google controls.** A head unit accepts only a phone identity that chains to Google's Automotive Link certificate authority, and Google alone issues those certificates. Gearslip does not ship one. Without it, Gearslip runs and renders correctly against a debug harness, but a real car rejects the connection. A leaked certificate exists that older head units accept; newer firmware and Google's reference tooling reject it. - **Gearslip needs no adb, root, or Shizuku.** Every feature relies on an ordinary Android permission or an on-device consent dialog. The two adb commands mentioned above, for audio, are the sole exception: both are optional, and both only remove a dialog that the driver would otherwise see once per drive. ## Building ``` ./gradlew :gearslip:assembleDebug ``` The APK lands at `build/Gearslip-debug.apk`. A release build needs a signing key. Copy `keystore.properties.example` to `keystore.properties`, fill in your own values, and run `./gradlew :gearslip:assembleRelease`. Git ignores both the properties file and the keystore. Without them, the debug build still works. ## Writing apps for Gearslip [docs/BUILDING_APPS.md](docs/BUILDING_APPS.md) specifies how to write apps that Gearslip can render: templated apps, media apps, and the Gearslip app protocol. ## License Gearslip is licensed under AGPL-3.0; see [LICENSE](LICENSE). The author offers a separate commercial license for private use outside the AGPL's terms; see [NOTICE.md](NOTICE.md).