I need to add custom validation to a form, lets says add article form.

I was expecting something like hook_FORM_ID_validate() to handle this, but cannot find anything relavant in the API documentation.

What is the way to add custom validation to a form?

2 Answers 2


You can add any number of validation functions to any form in hook_form_FORM_ID_alter() like so:

function mymodule_form_article_node_form_alter(&$form, &$form_state, $form_id) {
  // There will already be some validate handlers added so you need to add to the
  // array rather than overwrite it.
  $form['#validate'][] = 'mymodule_article_form_validate';

  // As mentioned above you can add as many as you want
  $form['#validate'][] = 'mymodule_article_form_validate_2';

function mymodule_article_form_validate($form, &$form_state) {
  // Random example, if the title is 'test' throw an error
  if ($form_state['values']['title'] == 'test') {
    form_set_error('title', 'Title cannot be "test"');
  • Suppose i've added custom form validation to a form which have already 2 validation function. Then which is get first preference in drupal 7?
    – Guru
    Sep 7, 2015 at 12:25
  • Which ever is first in the array @Guru
    – Clive
    Sep 7, 2015 at 12:26
  • If the form is user_registration_form, then it always keeps "[#validate] => Array ( [0] => user_account_form_validate [1] => user_validate_picture )". Suppose i'm going to add custom validation. Then it should be like this "[#validate] => Array ( [0] => user_account_form_validate [1] => user_validate_picture [2] => user_register_validate )". But i want to run "user_register_validate" function at first.
    – Guru
    Sep 7, 2015 at 12:36
  • For other fields, you got to use: if ($form_state['values']['field_custom']['und'][0]['value'] == 'Error') { //throw error } Apr 27, 2018 at 22:36
  • how to set validation for size, extension in this manner? And one more question, if there is ajax functionality like"upload" and "remove" how we handle validation for this?
    – steniya
    May 17, 2019 at 10:25

You should use hook_form_alter and add your function to the #validate property.

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