If you get the following error while trying to serve your Laravel project using artisan check the following common problems and make sure all of them are fixed.

bootstrap/../vendor/autoload.php. Failed to open stream: No such file or directory. The „vendor“ folder does not exist.

This error usually appears when you try to run „php artisan serve“ on your Laravel project before actually setting it up.

You did not fetch Laravel’s dependencies

Make sure to change to fetch Laravel’s dependencies after creating the project by running the following command

composer install

PHP Extension „php_mbstring“ is not installed

Check if you have installed and activated the PHP extension mbstring. It is needed by composer to download Laravel’s dependencies. This extension is included in every PHP installation, you just need to activate it by placing the following line in your php.ini file.

extension=php_mbstring.dll

Source: https://stackoverflow.com/questions/28468625/laravel-5-failed-opening-required-bootstrap-vendor-autoload-php