validate (check vars) (tag)

is_email()

Checks if the given string is an e-mail address.

rest_is_boolean()

Determines if a given value is a boolean or boolean-like. Doesn't look at the type of a given value, and like in PHP, 1 = true and 0 = false.

validate_file()

Checks the given string to see if it is a valid file path (file name). If the check passes, it returns 0; if not, it returns: 1, 2, or 3.

wp_http_validate_url()

Checks if the specified URL can be used in an HTTP request, for example in the HTTP API.

wp_validate_redirect()

Checks the specified URL for the possibility of using it for redirection.