Getting started

Cobalt is a lightweight HTML5/CSS/JS application container that is designed to provide a rich application development environment with minimal resource consumption (deployment size, RAM, CPU, GPU). At the same time, Cobalt enables a rich, low-latency user experience across a wide variety of platforms and devices.

Target audiences

Cobalt's documentation is written with two audiences in mind:

  • Porters enable Cobalt to work on other platforms by using Starboard, Cobalt's porting layer and OS abstraction, to implement the platform-specific functionality that Cobalt uses. Each Starboard module (memory, socket, thread, etc.) defines functions that must be implemented for the porter's platform.

  • Developers want to build applications in familiar environments with advanced debugging tools without having to worry about compatibility with a highly fragmented set of browsers. At the same time, they want to have full control over their codebase so that they can ship features for constrained platforms, like TVs, on time and without technical risk.

Benefits of Cobalt

Cobalt significantly reduces the cost of supporting a browser on non-standard and resource-constrained platforms. In addition, since Cobalt operates at a consolidated, versioned platform abstraction layer, its porting effort is man-weeks, and subsequent rebases are near-free.

These are some other benefits that Cobalt provides:

  • More platforms

    • Cobalt does not require platforms to support JIT compilation and can run on platforms that disallow execution of dynamically generated code.
    • Cobalt is a single-process application and does not rely on the ability to spawn multiple processes.
    • Cobalt precompiles a set of shaders that are sufficient to express all graphical effects, thereby accommodating platforms that cannot compile shaders at runtime.
    • Cobalt requires a compliant C++11 compiler, allowing it to reach platforms with toolchains that don't support the newest C++17 features.
  • Small footprint

    • Cobalt is optimized for memory. Its surface cache never exceeds a predefined budget, and it never creates duplicate layers, reducing the likelihood of out-of-memory crashes.
    • Cobalt's small binary is designed to take up as little space as possible. By supporting a subset of HTML5/CSS/JS, Cobalt's reduced package size even allows bundling of CJK fonts on low-end devices.
  • Reduced input latency

    • Cobalt produces consistent 60FPS animations by only supporting animation of properties that don't affect layout, like transform, and always running animations on a separate thread.
    • Cobalt is optimized to run on single-core CPUs, resulting in better input latency since the renderer and resource loader do not compete with layout operations.
    • On platforms that support GLES2, Cobalt avoids CPU painting by performing almost all rendering operations on the GPU.

Getting started


Porters should begin with the porting guide, which explains how to use Starboard, Cobalt's porting layer, to customize the platform-specific functionality that Cobalt uses. There are several reference documents to help porters customize configuration files and to implement module-specific functionality. The Testing with NPLB document provides an overview of Starboard's compliance test suite.


Developers can follow the setup instructions for Linux or RasPi to set up their Cobalt development environment, clone a copy of the Cobalt code repository, and build a Cobalt binary. The Cobalt support guide lists the HTML elements, CSS properties, CSS selectors, and JavaScript Web APIs that developers can use in their Cobalt applications.