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

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

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