Iam using the "ACF" plugin with "ACF to REST API". I found a solution for querying a custom field over REST API.

I inserted this into my functions.php:

add_filter( 'rest_{type}_query', function( $args ) {
    $args['meta_query'] = array(
            'key'   => 'my_field',
            'value' => esc_sql( $_GET['field'] ),

    return $args;
} );

Url: /wp-json/wp/v2/posts?field=test The wildcard {type} can be: post | user | comment | attachment | custom post type | taxonomy

This solution is not perfect. Once this code snipped is added, the filter works but if you go to /v2/{type} <-- which usually lists all, this stops working.

Any solution for that?

  • you should not be using esc_sql like that, esc_sql is only to be used in very specific circumstances, most people coding with WP will never need to use it. Otherwise is there a reason you're modifying all API queries, not just the ones that have field set? Why not use the existing parameters for meta queries instead of adding a new one?
    – Tom J Nowell
    Nov 8, 2022 at 17:38

1 Answer 1


I got that working :)

add_filter('rest_myRoute_query', function($args, $request) {
  $fields = array('myCustomField');

  foreach ($fields as $field) {
    if (! empty($request[$field])) {
      $args['meta_query'][] = array(
        'key'   => $field,
        'value' => esc_sql($request[$field]),

  return $args;
}, 10, 2);

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