Exercism is a free coding practice platform that offers exercises in 67 programming languages. Unlike competitive coding platforms that focus on algorithmic puzzles, Exercism emphasizes idiomatic code writing code the way experienced practitioners in that language would write it. Each exercise comes with a test suite, and your solution passes when all tests pass.
The mentorship model is what makes Exercism genuinely different. After submitting a solution, you can request feedback from a volunteer mentor who is an experienced practitioner in that language. The feedback focuses on code quality, idioms, and best practices rather than just correctness. This is closer to a real code review than anything else available for free.
For developers learning a new programming language, Exercism provides a structured way to build fluency through practice. The exercises are well-designed to introduce language features progressively, and the ability to see community solutions after completing an exercise is valuable for understanding different approaches.
For developers who want to improve their code quality in a language they already know, the mentorship track provides feedback that is hard to get otherwise. Having an experienced practitioner review your code and explain why certain approaches are more idiomatic is the kind of learning that usually requires a senior colleague or paid coaching.
Completely free. Mentorship is provided by volunteers. The platform is open source and funded by donations and sponsorships.