Atlassian provides plugin developers with a Software Development Kit (SDK). By using this SDK, developers can create plugins that extend the functionality of all Atlassian products. The SDK allows you to quickly connect and use the plugin development platform.
The Atlassian Plugin SDK makes your life easier by helping to do the following:
Build plugins for any Atlassian application with a single tool.
Create a plugin skeleton, specific to the Atlassian application you are developing for.
Download the application binaries, install your plugin, and start the application.
Dynamically re-install your plugin after changes during development. No restart required.
Write quality unit tests and integration tests.