Welcome to the Atlassian Developer Documentation. Using the Atlassian plugin software developer kit (SDK), you can create apps to extend Atlassian server applications like Jira Software, Jira Service Desk, Confluence, Bitbucket Server, and Bamboo.
We also offer a number of infrastructure tools to help you create, market and sell your apps. For example, thousands of customers visit the Atlassian Marketplace and the Atlassian Marketplace in-product every day, to find apps they may want to install.
If you meant to write an app for an Atlassian Cloud product then please see the following guides instead: