About
One challenge per day, and it is the same challenge for everyone. Borrowed from Advent of Code, but it runs all year instead of twelve days in December.
You write your solution in the browser and run it against the test cases in one of 11 languages: JavaScript, TypeScript, Python, PHP, Ruby, Java, Go, C++, C#, Rust and Swift. Code executes in a sandbox on the server, results come back in well under a second. Once you submit, every other solution to the same challenge becomes readable — which is usually more interesting than the challenge itself.
One challenge a day, identical for all users
11 languages, executed server-side in a sandbox
All solutions readable after you submit
Optional streaks, profile and leaderboard
No account needed to solve today's challenge
Free, non-commercial, open source (MIT)
40 challenges so far, so the rotation repeats after 40 days until I write more.