Here are several very useful HipChat Connect developer tools built and shared by various Atlassian developers:
Auto-complete and schema validation for your HipChat Connect add-on descriptor. Add new extensions to the HipChat Connect add-on descriptor effortlessly by using snippets for webhooks, actions, glances and any other module type. Need the JSON for an Activity card in your JS code? Use one of the card snippets included in this extension.
You can install this extension from here.
The HipConnect Tester is an add-on showcasing HipChat Connect's capabilities; It's the HipChat Connect kitchensink app. It allows you to play with API functionality, see how Cards, Glances, etc., look and grab the code as a starting point for your own project. You can install this add-on from here.