Salesforce Validation Rules
What Is Validation Rules?
A validation rule prevents a record from being saved unless it meets a condition you define, displaying a custom error message when it doesn't. It's the primary tool for enforcing data quality standards at the point of entry.
Why It Matters
Without validation rules, data quality depends entirely on user discipline -- and that never holds up at scale. A validation rule enforces the standard automatically, every time, for every user, regardless of how the record is being created (manually, via API, or through a flow).
How to Set It Up
Go to Setup, find the object, and click Validation Rules.
Click New and write the rule's logic using a formula that evaluates to TRUE when the record is invalid (this trips people up -- the formula describes the error condition, not the valid condition).
Write a clear, specific error message that tells the user exactly what to fix, not just that something is wrong.
Decide whether the error should attach to a specific field or display at the top of the record.
Activate the rule and test both a record that should pass and one that should be blocked.
Common Mistakes to Avoid
The formula-logic direction is the single most common point of confusion -- writing a rule that describes what's valid instead of what's invalid inverts the entire rule's behavior. The second common mistake is stacking too many validation rules on one object without testing how they interact, which can make legitimate edge-case records impossible to save.