Your Kobo can run apps now.

Cobalt is an open-source application platform for Kobo e-readers: a launcher, a signed App Store, a Rust SDK, and a runtime that keeps every app in its own unprivileged process.

Install it once over USB. Every app after that installs, updates and removes on the reader itself, over Wi-Fi. A reboot returns to the stock Kobo reader.

Install on your Kobo Read the source

The Cobalt launcher on a Kobo Clara BW showing Settings, App Store, Terminal, AI Chat, Audiobooks, Components, Daily Brief, Feeds and Gutenbird

The launcher on a Kobo Clara BW.

Not affiliated with Rakuten Kobo

Recorded on-device at 3× speed. Watch as video.

Running on a Kobo.

Every app is a static ARM binary running as its own unprivileged process on stock hardware. The App Store installs, updates and removes them over Wi-Fi, with signatures verified before anything launches.

arXiv papers and coding agents, on the panel.

These are photographs of the device, not simulator captures. The arXiv app reads the HTML rendering arXiv publishes for every paper since December 2023: abstracts, sections, math and result tables, paginated for the panel.

An arXiv preprint section titled 'A hard optimization problem and its relaxation' rendered on a Kobo Clara BW

A preprint, page 8 of 54, on the panel.

A results table from an arXiv paper comparing language models, rendered on a Kobo e-reader

A results table from the same paper.

$Mathematical notation and a numbered algorithm from an arXiv paper on a Kobo e-reader$

Math notation and a numbered algorithm.

Sidekick on a Kobo showing a question from Claude Code with three tappable answers and a 'Leave it for the terminal' button

Sidekick showing a question from Claude Code, with tappable answers.

Sidekick's watching screen on a Kobo, paired with a machine on the local network, showing the last answer sent

Sidekick paired over the local network, waiting for the next question.

Apps

The apps.

Every screenshot below is a capture from a Kobo Clara BW. 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.

Audiobook Studio

Researches, writes, narrates and plays an original audiobook.

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.

AI Command Center

Asks a question and turns the answer into touch-friendly reading.

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 →

The Cobalt App Store installing an app over Wi-Fi on a Kobo Clara BW

Sudoku arriving over Wi-Fi.

FIG. 1 CLARA BW N365

Install

Installing from source.

1. Charge a Kobo Clara BW (N365) and connect it over USB. Other models are refused, not guessed at. 2. Run the setup:

git clone https://github.com/BandarLabs/Cobalt.git
cd Cobalt
rustup target add armv7-unknown-linux-musleabihf
cargo run -p kobo-cli -- setup

1. Restart the reader and open Cobalt from Kobo's menu. 2. 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.

1. Build it. Add the app as a workspace package under `apps/<app-id>/` and register it in `apps/catalog.json`. 2. Test it. Add unit and layout tests, and run it in the browser and runtime simulators. 3. Run it on your own device. A real Clara BW, not just the simulator. 4. 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.

Your Kobo can run apps now.

Your Kobo can run apps now.

Your Kobo can run apps now.

Running on a Kobo.

arXiv papers and coding agents, on the panel.

The apps.

An app is one Rust file.

Signed packages, verified before launch.

Installing from source.

Contribute an app.

Device support and safety.

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