Cobalt: apps and an SDK for Kobo e-readers

Store apps version independently of the platform; the rest ship with the platform install. Launcher Opens installed apps and always keeps a route back to the Kobo reader. App Store Installs, updates, removes and reinstalls signed apps over Wi-Fi. arXiv Browses a subject's newest preprints and reads the full text on the panel. Sudoku Store-only by design: installing it proves delivery of an app the USB package never contained. Morse Sends a typed message in Morse on the front light, one letter across the whole panel. Gutenbird Reads any OPDS library: Project Gutenberg, Standard Ebooks, Open Library, or yours. Hacker News Top, New, Ask and Show stories with complete comment threads. Feeds Discovers a site's feed and presents its articles without the site's layout. Daily Brief Collects the day's stories in the background while you use another app. Sidekick Approve or deny requests from coding agents, away from the keyboard. Terminal A panel-native shell with keys that send input immediately. Components The UI toolkit's controls, layouts, typography and states, on the panel. Settings Connectivity, hardware, and platform updates, kept separate from Store. Todo A persistent list with touch entry and completed-item states. Tic-tac-toe Two players, partial refreshes for individual cells. Magnet Locates the hall sensor behind the bezel and reports its changes. The SDK An app is one Rust file. Implement KoboApp, describe screens declaratively, and the runtime handles layout, e-ink refresh planning, Back navigation and lifecycle. Apps don't open device resources; they ask. Network, storage, audio, frontlight and Wi-Fi are capability-gated, and a refusal comes back as a value the app can handle. E-ink UIText, tiles, dialogs, keyboards, pagination, partial refresh planning SimulatorsBrowser and runtime simulators with layout diagnostics Async workHTTPS, ranged downloads, cancellable tasks, scheduled wakes StateAtomic per-app keyed storage ShippingSigned static ARMv7 binaries, published when an app PR merges kobo new my-app cd my-app kobo dev Read the SDK docs use kobo_sdk::{ ActionId, Context, KoboApp, ScreenBuilder, }; #[derive(Default)] struct Hello { taps: u32 } impl KoboApp for Hello { fn on_start(&mut self, ctx: &mut Context) { self.show(ctx); } fn on_action( &mut self, ctx: &mut Context, a: ActionId, ) { if a == kobo_sdk::action_id("tap") { self.taps += 1; } self.show(ctx); } } impl Hello { fn show(&self, ctx: &mut Context) { let screen = ScreenBuilder::new("hello") .top_bar("Hello") .heading(format!("{} taps", self.taps)) .button("tap", "Tap me") .build(); ctx.set_screen(screen); } } fn main() { let app = Hello::default(); let _ = kobo_sdk::run("hello", app); } The Store Signed packages, verified before launch. Store reads a signed catalog from a fixed GitHub release. Each package holds one ARM executable and a signed canonical manifest. The runtime verifies the catalog, the package, the installed manifest and the binary before an app runs. App releases are independent of platform releases: merging an app PR builds it for ARM, signs it, and updates the catalog. No Cobalt version bump, no reinstall. The app simply appears in Store. The Cobalt platform itself also updates over Wi-Fi, through Settings, on a channel separate from the app catalog. The USB cable is only ever needed once. Install and catalog transactions are recovery-safe; an interrupted update leaves the reader with the version it had. Publish your own app → Sudoku arriving over Wi-Fi. Install Installing from source. Charge a Kobo Clara BW (N365) and connect it over USB. Other models are refused, not guessed at.

Open Store. Everything from here on arrives over Wi-Fi. The complete walkthrough, including recovery steps, is in docs/INSTALL.md. Contributing Contribute an app. App contributions are regular pull requests. If it runs on your device and the PR shows it running, it gets merged and published. Build it. Add the app as a workspace package under apps/<app-id>/ and register it in apps/catalog.json. Test it. Add unit and layout tests, and run it in the browser and runtime simulators. Run it on your own device. A real Clara BW, not just the simulator. Open a PR with a gif or photos of it running. Once reviewed and merged, the publish workflow signs it and it appears in Store. No platform release needed. Own a different Kobo model? Porting is welcome too; open an issue first so the device profile can be agreed. Full details in docs/CONTRIBUTING_APPS.md. Safety Device support and safety. Cobalt does not replace Kobo's boot chain. Device writes are gated on an exact hardware and firmware match, and a reboot returns to the stock reader. The first installation does modify files on the user storage partition, and it is provided without warranty. Only the Clara BW profile has been hardware-tested. Don't install on another model until it has a reviewed, hardware-tested profile. Cobalt is an independent project, not affiliated with Rakuten Kobo.