snipe-it/app/Http/Requests/CustomFieldRequest.php

<?php

namespace App\Http\Requests;

use Illuminate\Foundation\Http\FormRequest;

class CustomFieldRequest extends FormRequest
{
    /**
     * Determine if the user is authorized to make this request.
     *
     * @return bool
     */
    public function authorize()
    {
        return true;
    }

    /**
     * Get the validation rules that apply to the request.
     *
     * @return array
     */
    public function rules()
    {
        return  [
            "name" => "required|unique:custom_fields",
            "custom_format" => "valid_regex",
        ];
    }
}