Contact
One address, read by a person.
A challenge is wrong or confusing
Use the Report a problem button on the challenge itself — it attaches which challenge you meant, which saves a round of back-and-forth. Email works too.
Delete my account
Email from your registered address and everything goes: attempts, submitted code, progress and bookmarks. See the privacy policy for exactly what is stored.
I want to suggest a challenge
Very welcome. The most useful suggestions are bugs you actually hit — the ones that cost you an afternoon. Send the buggy code, what you expected, and what happened instead.
I teach, and want to use this with a class
Please do; it is free and needs no licence. Get in touch if there is something specific that would make it work better for a class.