Protohackers
Build network servers from a spec and let a checker test them
Protohackers is a server programming challenge. Each problem gives you a protocol spec. You write a network server that follows it, run it somewhere the internet can reach, and submit its address. An automatic checker then connects to your server and tests it, and the fastest solvers appear on a leaderboard.
Free · Login needed · Server · Intermediate
About Protohackers
The problems train you to read a spec carefully and build network servers that really work. It suits developers with some backend experience who want to go beyond web frameworks.
You can use any language you like. You need a server with a public address, and you log in with a link sent to your email. James Stanley started the project in 2022.
On Breakpoint since 23 Oct 2026.