Validators check the field value of the issue and reject the transition if the criteria are not met. The following workflow validators were initially provided by the JSU app but are now maintained for Jira Cloud by Atlassian:
Regular Expression Check
To add a validator to your workflow rule:
Open a draft version of your workflow.
Select your transition, then select the Validators tab. Existing validators for the transition are listed.
Select Add Validator to choose a validator.
Choose the required validator, then select Add.
To learn more about workflow validators in Jira, see Atlassian'sJira documentation. Our Workflow Validators documentation for JSU on Jira Server/Data Center may also provide some hints on how to configure them in Jira Cloud.