How can I make Laravel return a custom error for a JSON REST API

go to your app/start/global.php.

This will convert all errors for 401 and 404 to a custom json error instead of the Whoops stacktrace. Add this:

App::error(function(Exception $exception, $code)
{
    Log::error($exception);

    $message = $exception->getMessage();

    // switch statements provided in case you need to add
    // additional logic for specific error code.
    switch ($code) {
        case 401:
            return Response::json(array(
                    'code'      =>  401,
                    'message'   =>  $message
                ), 401);
        case 404:
            $message            = (!$message ? $message = 'the requested resource was not found' : $message);
            return Response::json(array(
                    'code'      =>  404,
                    'message'   =>  $message
                ), 404);        
    }

});

This is one of many options to handle this errors.

---

Making an API it is best to create your own helper like Responser::error(400, 'damn') that extends the Response class.

Somewhat like:

public static function error($code = 400, $message = null)
{
    // check if $message is object and transforms it into an array
    if (is_object($message)) { $message = $message->toArray(); }

    switch ($code) {
        default:
            $code_message = 'error_occured';
            break;
    }

    $data = array(
            'code'      => $code,
            'message'   => $code_message,
            'data'      => $message
        );

    // return an error
    return Response::json($data, $code);
}

You can pass an array to the returned JSON response:

$returnData = array(
    'status' => 'error',
    'message' => 'An error occurred!'
);
return Response::json($returnData, 500);