Find Workflow Rules for Jira at Atlassian Marketplace. Install the add-on by following the standard steps. No configuration is needed at the moment.
Log into Jira application with administrator permission.
Navigate to Issues - Workflows in Jira administration.
Edit the workflow and select the transition for which you want to define rules.
Click “Add condition“ under Conditions tab.
Select “Generic Rule Condition“ and click “Add“.
The editor shows up and you can start editing. If you have no idea what to type, just simply press space.
Once completed, click “Add“ to submit the work.
The defined rule should show up under the condition tab. Don’t forget to publish the change otherwise the rules will not be picked up by the workflow.
The same steps work for validator and post-function.