Validation should always be done both on the browser and server side. The browser can catch simple failures like mandatory fields that are empty and when you enter text into a numbers only field. These can however be bypassed, and you should make sure you check for these validation and deeper validation server side as failing to do so could lead to malicious code or scripting code being inserted into the database or could cause undesirable results in your website.
Validation should always be done both on the browser and server side. The browser can catch simple failures like mandatory fields that are empty and when you enter text into a numbers only field. These can however be bypassed, and you should make sure you check for these validation and deeper validation server side as failing to do so could lead to malicious code or scripting code being inserted into the database or could cause undesirable results in your website.