Validation rule execution timing
Key Takeaway
Validation rules run after before-save flows and before triggers, and before the record is saved to the database. They don't run for workflow field updates or process scheduled actions.
A validation rule is a formula that checks a record's data when the record is saved. If the formula returns True, the rule blocks the save and shows an error message. Two things decide whether automation can cause a validation error, fix one, or slip past one: where validation rules sit in the save sequence, and which kinds of saves skip them.
What happens when a record is saved
Validation rules run at save time. When a user clicks Save, Salesforce checks all validation rules. If all data is valid, the record saves. If any rule returns True, its error message shows, and the record isn't saved until the user fixes the data and saves again.
One failing rule doesn't stop the check. When one validation rule fails, Salesforce keeps checking the other validation rules on that field or other fields. The user then sees all the error messages at once.