Before add to card in woocommerce if you need to custom validation than you can use woocommerce action woocommerce_add_to_cart_validation
by this action you can use validation.
there is 5 arguments. lets we understand one by one.
$true indicated to validation is true or false value
$product_id get product id which request for add to cart
$request_quantity get product qty
$variation_id that get to if variation id available than get it
lets we understand with example . we assume minimum item qty should be 10
this way you can be easy to understand how to work woocommerce_add_to_cart_validation action