Codeforces vs Judge0 CE

Codeforces exposes a JSON API over its own contest and user database, covering problems, contests, submissions, ratings, and hacks through methods like contest.standings, user.info, and problemset.problems. Most methods are fully public and callable with no key at all — a live call to user.info returned real rating and rank data with zero authentication — while a handful of privacy-sensitive methods (e.g. user.friends) require a signed apiKey/apiSig pair generated from a registered account. There's no paid tier or usage fee; the service is entirely free.

Judge0 CE is an open-source sandboxed code-execution engine, and ce.judge0.com is its free public demo instance covering 60-plus compiler/language versions via a REST API for creating and polling submissions. A live, fully unauthenticated request — no token, no key — both listed supported languages and executed a real Python submission end-to-end, confirming the public instance ships with authentication disabled by default. Judge0's own docs steer production users toward a paid RapidAPI-hosted plan or self-hosting instead, but the tracked ce.judge0.com endpoint itself remains free to call directly.