uuidv4.link
uuidv4.link/txt
uuidv4.link/json

Alternatives

This site is not novel.

Top Google Search result for "uuid generate online": www.uuidgenerator.net/ (this one works just fine, and has support for generating a whole bunch of uuids at once)

Or do you have access to a unix command line? Depending on your distro, you may have uuidgen which would be fewer keystrokes than opening up a website.