Prevent duplicates in text custom field

[AbrahamA]

Hello

I have a custom field which is single line text field. I need to make sure there are no duplicate values entered in that text field

What is better to do

write a validator in which runs jql and checks

or

is there a better way to do like a behavior or something else

Thanks

Abe

[Brant Schroeder]

@AbrahamA 

There is not a delivered validator that provides this functionality.  If you have the app JSU or Scriptrunner I believe you can do this.