Exercism
exercism.org
Practice exercises in 80-odd languages with free feedback from a human mentor
Free account
Loading page
freecodecamp.org
Teaches web development by making you write code in the browser from lesson one.
A few thousand small coding challenges, each written and run in an editor inside the page, grouped into certifications like responsive web design, JavaScript algorithms and data analysis with Python. Every certificate is gated on building five working projects, which is why people finish it: you leave with something to show rather than a completion percentage. It is deliberately practice-first, so explanations are short and you will have MDN open alongside it.
Questions
Free to use, but you have to register before it will do the job. You need a free account to save progress, and the certificates are portfolio evidence rather than accredited qualifications.
Yes. freeCodeCamp sends your input to its own servers to process it. That is fine for public material; for anything containing personal data, use one of the on-device tools instead.
You need a free account to save progress, and the certificates are portfolio evidence rather than accredited qualifications.
Alternatives
Same category or same task, ordered by how closely they overlap.
exercism.org
Practice exercises in 80-odd languages with free feedback from a human mentor
apps.ankiweb.net
Schedules flashcard reviews for the day before you would have forgotten them
khanacademy.org
Explains school maths and science one short video and one exercise at a time
duolingo.com
Turns a language into five-minute daily drills you will actually keep doing
ocw.mit.edu
Publishes the real lecture notes, problem sets and exams from MIT courses
monkeytype.com
A typing test you can tune to the exact words, punctuation and length you want