The first save after I turned on a new website rule failed, and it wasn’t even a website edit. I changed only the Phone on Burlington Textiles Corp of America, an old sample account, and Salesforce refused: “Enter the full secure address, starting with https://”. The account had held www.burlington.com for years. My rule was correct for new data and wrong for every old record that already broke it.
These are the rules I now follow for validation rules in Salesforce, each one tested in a Winter ’27 Developer org. You’ll get the plain-words definition, the exact clicks to create a rule, five formulas you can copy, and the checks that keep a new rule from blocking the sales team on day one.
Learn what a validation rule blocks before you write one
A validation rule is a formula that Salesforce runs when someone saves a record. If the formula returns TRUE, the data is bad: the save stops and