Expression Validators & Conditions for Jira runs on Atlassian Forge.
Data stored by the app. None. Rule settings (field ids and names, status names, values, your error message) are saved by Jira in the workflow, through Atlassian's workflow rule API. They contain no personal data unless an admin types it into a rule.
Data read. The field list and issue link types (to fill the form), and, when an admin clicks Test against issue, the result of evaluating the rule on that issue. These calls are made as the signed-in admin, and the results are shown only to that admin.
Data sent outside Atlassian. None. The app declares no external hosts.
Logs. The app logs only a short error name when a Jira request fails. It logs no issue content.