<?php

namespace App\Http\Requests;

use Illuminate\Contracts\Validation\Validator;
use Illuminate\Http\Exceptions\HttpResponseException;
use Illuminate\Foundation\Http\FormRequest;

/**
 * Class MyRequest
 * @package App\Http\Requests
 */
class MyRequest extends FormRequest
{
    public function rules(): array
    {
        return []; // your rules here
    }

    protected function failedValidation(Validator $validator)
    {
        throw new HttpResponseException(response()->json([
            'status' => 'ERROR', // anything you like
            'errors' => $validator->errors()
        ], 422));
    }
}

If you are building a REST API then add the headers Accept: application/json to your request.