Glossary Guide
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Glossary of Terms


App / Application

An application which executes on a Fitbit device. The application is comprised of JavaScript (.js) or TypeScript (.ts) files for the application logic, SVG (.gui) files for the structure, and CSS (.css) files for the presentation layer.

Clock face

Clock faces are a special type of app that are primarily used to display the current date and time. Each device has a single clock face installed at any time, and interaction is limited to touch events only.

Device API

A set of JavaScript APIs which allow developers access to data from hardware sensors, send and receive communications, or interact with the presentation layer of the device. These APIs are only accessible within application code. Read more.

SVG (Scalable Vector Graphics)

SVG defines the structure of your application’s presentation layer. Read more.


Prebuilt, easy to use SVG components which can be included in your application. Some examples include: Clock, Menu Bar, Button etc. Read more.

CSS (Cascading Style Sheets)

CSS is used to apply styling to your application’s presentation layer. It allows you to change colors, fonts, positioning and sizes of elements. This is based up standard web CSS, but it does have a few subtle implementation differences. Read more.


A secondary JavaScript application, which executes within the Fitbit mobile application. The companion can act as a bridge between the Fitbit device and the Internet. It allows you to send and receive data or files, or perform data processing without the constraints of the Fitbit device hardware.

Companion API

A set of JavaScript APIs which allow developers to send and receive communications, or utilize the processing capabilities of the mobile device. These APIs are only accessible within companion code. Read more.


Settings allow users to change the behavior or appearance of an application by changing values from within the Fitbit mobile application. Settings are comprised of components such as text boxes, toggles, select lists and other form controls.

Settings API

The Settings API is used to generate an application's settings page. Each setting can be easily defined using React JSX, and the Fitbit mobile application will render this as a form which matches the existing appearance of the mobile application.

Fitbit Studio

Fitbit Studio is the web browser based environment used for Fitbit application development. Developers can create, edit and compile multiple applications using this online tool.

Developer Bridge

The Developer Bridge provides a websocket connection between Fitbit Studio, your Fitbit device, and the Fitbit mobile application. This connection is used to install apps and companions, and provides console logs to Fitbit Studio.