json-api-server/docs/filtering.md

Filtering

You can define a field as filterable to allow the resource listing to be filtered by the field's value.

This works for both attributes and relationships:

$type->attribute('firstName')
    ->filterable();
// GET /users?filter[firstName]=Toby

$type->hasMany('groups')
    ->filterable();
// GET /users?filter[groups]=1,2,3

The >, >=, <, <=, and .. operators on attribute filter values are automatically parsed and applied, supporting queries like:

GET /users?filter[postCount]=>=10
GET /users?filter[postCount]=5..15

Custom Filters

To define filters with custom logic, or ones that do not correspond to a field, use the filter method:

$type->filter('minPosts', function ($query, $value, Context $context) {
    $query->where('postCount', '>=', $value);
});

Just like fields, filters can be made conditionally visible or hidden:

$type->filter('minPosts', $callback)
    ->visible(function (Context $context) {
        return $context->getRequest()->getAttribute('isAdmin');
    });