The plain-English version
A rule enforced by the database to restrict which records are valid.
Why it matters
It protects data even when multiple applications or direct writes bypass the interface.
Let’s make it click
A uniqueness constraint prevents two accounts from using the same normalized username.
Vibe Bro’s heads-up
Friendly form validation is still useful, but it cannot replace a database rule when concurrent writers must preserve an invariant.
The docs behind it
Documentation links checked .
Editorial review · October 28, 2026
Supported: Database constraints protect concurrent writers independently of UI validation; uniqueness example assumes the normalized value is stored or indexed.