You need don't anything special to install, only Composer.
Download and installation instructions of Composer.
After install Composer please run the following:
composer install
You will need only of PHP 7+.
In terminal, root directory:
php -S 0.0.0.0:8081
And in a browser please open the address http://127.0.0.1:8081
In the browser you will see this page:
Then you can use a textbox and click at the button in this right position. Ilustrating:
Case you insert a wrong string to convert you will see an error:
Please run through this command in the root directory:
composer test
If you face an autoload error, please run the following command:
composer dump-autoload -o