Karabiner

Karabiner is a keyboard customization tool for macOS that enables users to remap keys, alter keyboard behavior, and apply complex input rules. It originated as KeyRemap4MacBook in the early 2010s and was later renamed Karabiner. Development later split into Karabiner-Elements, a modern rewrite designed to support recent macOS versions and Apple Silicon.

Its architecture includes a background service that intercepts keyboard events, a configuration format based on JSON, and a graphical user interface for managing profiles, devices, and rules. Users can create simple one-to-one remappings or complex modifications that are conditional on the active application, the state of modifiers, or sequences of keystrokes. A library of complex modifications lets users apply rules shared by the community.

Configuration is stored in a karabiner.json file (in the user's configuration directory), and can be edited directly or through the GUI. Common uses include remapping Caps Lock to Escape, swapping Command and Option, or implementing multi-key shortcuts. Rules can be enabled per application or per device, enabling tailored setups for different workflows.

Karabiner-Elements is the current and actively maintained version; Karabiner remains a widely used tool in macOS power-user communities. It is open-source and available on GitHub under a permissive license.