Client-Side Validation

noun

say it: “KLY-ent SYDE val-ih-DAY-shun” /ˈklaɪənt saɪd ˌvælɪˈdeɪʃən/

Checking form input in the browser before it is sent, so the user sees mistakes straight away.

What is Client-Side Validation?

Client-Side Validation — Checking form input in the browser before it's sent, so the user sees a mistake straight away. It's for convenience only: anyone can skip it, so the server checks again.

<input type="number" name="price" min="0" required>

In a sentence

• “Client-side validation told me the email was missing before the page even posted.”

Level: Apprentice · More Web Development terms at this level

Updated October 28, 2026