This is a very simple web server that allows you to construct and preview Java SimpleDateFormat-formatted date and time, which is useful for development and localization purposes. Since it is written in Java, it is guaranteed to give you a canonical output, unlike SimpleDateFormat-compatible implementations available for other languages. It looks like this:
Provided you have Java installed, you can compile and run the server by using the supplied script:
$ ./run-server
Then open http://localhost:8000/ to open the web page.