Adding field validation to Sitecore editor

Sometimes you may want to add validation to a field on Sitecore, like limiting the length of a text field. Sitecore comes with some sample field validations that you can add to your templates, or duplicate and modify to create new ones.

In the Sitecore Content Editor, go to sitecore > System > Settings > Validation Rules > Field Rules > Sample to see the pre-packaged rules. I wanted to create a Max Length 55 rule, so I duplicated one of the existing Max Length rules and changed the name, title, Description, and the Data Parameters to have that 55 value. Save and publish the rule.

Then go to Templates and expand the template until you can select the actual field in the left sidebar tree. In the right side, go down to the Validation Rules section, Validator Bar, and find the new rule you made in the Sample folder. Click to select, then click the ">" button to select it. Adding the rule to the validator bar will highlight the field in red if trying to save while the field is too long.

Save and publish the changes on the template, and you're done!