Need help with development of a plugin

I’ve been tasked with the creation of a jira plugin for a university project. It’s supposed to analyze the contents of the description field during issue creation and somehow display the result to the user before they press the 'Create" button or show the result in a popup window as they press the ‘Create’ button.
I’d appreciate it if you could link me some examples of ways this might be implemented, or at least point me in the right direction.
I’m asking for help because I never developed any plugins for jira, and my time constraints are very tight and so far I wasn’t able to find anything of use.
Thanks in advance.

A web resource module defined in a plugin could add Javascript to the Issue Create dialog:

If Javascript is appropriate for your use-case, you could bind to the Description field’s blur event, perhaps.