On April Fools in 2021, the popular xkcd comic ran Checkbox, which was a Morse code puzzle in disguise. (It’s interesting to see the community trying to figure out what it actually does.)

Engineer Max Goodhart built the front-end and wrote a summary of the whole project:

This year was a doozy. We specced and scrapped several different ideas in the months leading up to today. We finally settled on today’s concept just 3 days ago. The need to do something simple was a really useful constraint, and we leaned into the idea of making something primitive but deep.

The team seems to have had a lot of fun with it, including even JavaScript being encoded in Morse Code (the link in the blog post no longer works, but you can still see it on the Internet Archive).

Goodhart also wrote about the immense challenge of adjusting the Morse tapping speed to the user, which counterintuitively ended up needing… adjusting the user to the speed. But the best part is that the server communications used the Morse code in URLs, as well:

We took great pains to make the API for this project use morse code in the transport. If you take a look at the network inspector, you’ll notice that the URLs requested have morse code in them.

This worked for every combination of letters imaginable, with two oddly specific exceptions: a solitary E, and a solitary I.

I liked this description of what transpired next, which would have made me think I was going insane, too:

Then, an even stranger thing happened. I copied and pasted the correct URL into my browser and pressed Enter, and right before my eyes, it deleted the ”.” from the end of the URL and returned a different result.

I was delighted to discover an answer here, not only because in retrospect it’s such an obvious thing that was staring us all in the face for decades, but also because it has interesting URL construction consequences.