Add CSS Class to fields

No, there are no filter for class. Instead, you can probably utilize wpcf7_form_tag filter you can find in the includes/shortcodes.php file for such purposes.

Thanks for purposes,

by dumping the $tag array by this code :

add_filter( 'wpcf7_form_tag', 'dump_wpcf7_form_tag_filter' );
function dump_wpcf7_form_tag_filter( $tag ) {
  if ( ! is_array( $tag ) )
  return $tag;
  echo "<pre>";
  var_dump($tag);
   echo "</pre>";
  return $tag;
}

( PS: if you test the code, the result are double, it like do_shortcode_tag() is executed two time ?)

I was made many tests, and i see that the css class for all components is returned by wpcf7_form_controls_class.

i suggest adding a filter in wpcf7_form_controls_class function, this will make adding css class more easy.

Reagrds,

so if i was to add code to functions.php for bootstrap 3. How would i go about it?
Ex. adding class “checkbox” to <input type="checkbox">.