Kobo e-readers can now run third-party apps
Cobalt platform brings app functionality to Kobo devices
1What is Cobalt?
Cobalt is an open-source application platform designed for Kobo e-readers. It consists of a launcher, a signed app store, a Rust SDK, and a runtime that runs each app in its own unprivileged process. The initial setup is done via USB, while all subsequent apps can be installed and updated over Wi-Fi. The system verifies each app's signature before execution to ensure security.
2How it works
On the Cobalt platform, each app runs as a static ARM binary in its own unprivileged process on standard hardware. The App Store manages installation, updates, and removal over Wi-Fi. When the system reboots, it returns to Kobo's standard e-reader interface. Apps cannot directly access device resources; they must request authorization for features like network, storage, and audio.
3App ecosystem
The Cobalt app store is fed from a signed catalog published on GitHub. Each package contains an ARM executable and a signed manifest. App versions are independent of platform versions - when an app PR is merged, it's compiled for ARM, signed, and the catalog is updated. Users don't need to reinstall the platform to see new apps in the store.
4Developer experience
The Cobalt SDK is written in Rust and allows developers to create apps by implementing the KoboApp trait. Apps declaratively define screens, while the runtime handles layout, e-ink refresh planning, and navigation. Developers can use the 'kobo dev' command to test their apps and submit PRs to have them added to the store.
5User experience
After installing Cobalt, users can read arXiv papers, access OPDS libraries, create original audiobooks, and send Morse code messages. Apps can collect data in the background and update while the user is in another app. The interface is fully panel-native and optimized for touch interactions.
6Security and limitations
Cobalt doesn't modify Kobo's boot chain, and device writes are limited to exact hardware and firmware matches. Currently, only the Kobo Clara BW model has passed hardware testing. The platform is an independent project with no official connection to Rakuten Kobo. Users should wait for hardware-tested profiles before installing on other models.
7Community contributions
As an open-source project, Cobalt encourages community contributions. App contributions are accepted via normal PRs, and apps demonstrated to work on devices are merged. Developers wanting to port to different Kobo models should first open an issue to agree on device profiles. The full contribution process is documented.
8Impact on the e-reader market
Cobalt's release significantly expands the functionality of e-readers. Such open platforms for traditionally closed systems can extend device lifespan and better adapt to user needs. Support for arXiv and OPDS provides major advantages for academic and technical users. This development is seen as an innovative step in the e-reader market.