add_filter('cred_form_validate','chr_validation',10,2);
function chr_validation($field_data, $form_data)
{
    //field data are field values and errors
    list($fields,$errors)=$field_data;
    
    //check if post_title field is more than 500 words
    if ( str_word_count($fields['post_content']['value']) > 500 )
    {
        //set error message for post_content field
        $errors['post_content']='500 word count exceeded. Please, use less words for your description.';
    }   
   
    //return result
    return array($fields,$errors);
}