Custom Metadata Type Validation Rules

Validation rules verify that the data a user enters in a record meets the standards you specify before the user can save the record. A validation rule can contain a formula or expression that evaluates the data in one or more fields and returns a value of “True” or “False”. Validation rules also include an error message to display to the user when the rule returns a value of “True” due to an invalid value.

• Custom Metadata Type Fields and Validation Rules
  You can use validation rules with fields in custom metadata types, including relationship fields. Keep these tips in mind as you do.
• Custom Metadata Types and Validation Rule Formulas
  Use custom metadata records to store validation rule record values. Then, reference the records directly within validation rules and eliminate the need to add the same values into different validation rules. Using packaging? You can define the logic and leave customization to a subscriber.