# What is Extension API?

EasyEDA Professional Extension API (hereinafter referred to as "Extension API") is a set of JS API interfaces built on the front-end, which is used to develop various custom functions of EasyEDA Professional Editor. In short, the Extension API uses the basic syntax of JavaScript to write source code that highly encapsulates many EasyEDA Pro features and algorithms, together with a comprehensive [SDK](./ancillary-projects/pro-api-sdk), [type constraints](./ancillary-projects/pro-api-types), the development of custom extensions can be completed with very little effort, effectively reducing the mental burden on developers and designers.

Next, you can go to the [How to Get Started](./how-to-start) section to learn how to install the environment from scratch and build your own EasyEDA Pro Edition extension.

If you are an extension user, see the [Getting and Using Extensions](../user-guide/using-extension) section.
