I am using JSON API module to expose data using REST API. I want to alter its response. I am trying to altering it using hook_ENTITY_TYPE_load. If I change any existing property it shows the updated value. But if I try to add custom property it doesn't show the custom property in response. The two hooks I used are below:

function my_custom_entity_type_alter(array &$entity_types) {
  $entity_types['node']->set('flag_count', 10);

function my_custom_node_load($nodes) {
  foreach ($nodes as &$node) {
    $node->flag_count = 10;

I need to know if there is any possible way to alter the json api response with custom properties?

  • Is flag_count a valid typed data property on the node? That might be removed by serialization.
    – mradcliffe
    Jan 2, 2017 at 13:42
  • Did you add your custom property as a custom (computed?) field of the node entity?
    – Eyal
    Jan 2, 2017 at 18:13
  • @mradcliffe yes I tried the hook according to Neograph734 answer. I guess you are right, JSON API is removing the property. Need to debug the code. Jan 3, 2017 at 5:43

3 Answers 3


Please see how jsonapi_entity_base_field_info adds a computed property to the file entities. That should do.

If you don't want to create a virtual field, you can add a normalizer that only acts for that specific content type as a service. You'll need to use a higher priority than serializer.normalizer.entity.jsonapi (set to 21). Your custom normalizer can inherit from Drupal\jsonapi\Normalizer\ContentEntityNormalizer and add your custom stuff in getFields.

  • Thanks hook_entity_base_field_info worked like a charm!! :) Jan 4, 2017 at 11:10
  • Hi e0ipso, did you actually manage to alter the output of jsonapi module creating a new normalizer? Jan 22, 2019 at 12:00
  • 3
    Things have changed quite a lot since this comment was written. Take a look at lullabot.com/articles/jsonapi-2
    – e0ipso
    Jan 23, 2019 at 12:43
  • Long story short, the comment above is referring to the fact that you cannot override field normalizers from JSON:API anymore. You will get an error about it because the module considers normalizers part of internal API. There is a dirty trick that JSON:API Extras uses to get around this for its purposes -- it places code in the JSON:API module namespace to dodge the check -- but this is not a recommended pattern because the internal API of JSON:API could change at any time.
    – GuyPaddock
    Jul 26, 2021 at 1:55

You can create your own custom normalizers to alter the JSON response.

Some good resources:


I suppose you should be using hook_entity_type_build rather than hook_entity_type_alter, which states:

Do not use this hook to add information to entity types, unless one of the following is true:

  • You are filling in default values.
  • You need to dynamically add information only in certain circumstances.
  • Your hook needs to run after hook_entity_type_build() implementations.

Use hook_entity_type_build() instead in all other cases.

And EntityTypeInterface states

Additional information can be provided by modules: hook_entity_type_build() can be implemented to define new properties, while hook_entity_type_alter() can be implemented to alter existing data and fill-in defaults.

You might want to try something like this instead:

function my_custom_entity_type_build(array &$entity_types) {
  /** @var $entity_types \Drupal\Core\Entity\EntityTypeInterface[] */
    ->set('flag_count', 10);
  • Great. I can see the property in hook_ENTITY_TYPE_load but I guess JSON API removed this property. I need to debug some json api code itself. Jan 3, 2017 at 5:42

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