Can we create custom validation on an existing field while creating an issue

[Bhaskara Rao]

I am planning to create a validation script for an existing field like "Summary" field to validate the particular string is existing or not. this validation should be happen before creating an issue

[Vishal Biyani]

In the workflow transition to Open (or your starting status), you can add a regular expression validator

Steps to follow (Need JIRA Admin permission)

1.  Click on Edit Workflow
2. On Create step, click on it and you would see Validators on the right side
3. Click on Validators and then Add Validator
4. Use Regular Expression Check against the field. if the regex does not match, then issue won't be created.