What are the best free tech explainer sites for learning programming concepts and working through exercises?

Here are some of the best free tech explainer sites for learning programming concepts and practicing with exercises:

Best overall

• freeCodeCamp — Excellent for structured learning, hands-on coding exercises, and full curriculum paths. Great for beginners and intermediate learners.
  https://www.freecodecamp.org/

Strong concept explainers

• MDN Web Docs — Best for web development fundamentals: HTML, CSS, JavaScript, DOM, APIs. Very reliable and thorough.
  https://developer.mozilla.org/
• The Odin Project — Free full-stack curriculum with lots of guided projects and exercises. Good if you like learning by building.
  https://www.theodinproject.com/
• CS50 by Harvard — High-quality intro to computer science with lectures and problem sets. More academic, but excellent.
  https://cs50.harvard.edu/x/
• GeeksforGeeks — Huge library of explanations, examples, and practice problems. Quality varies, but useful for quick references.
  https://www.geeksforgeeks.org/

Great for interactive practice

• Exercism — Practice coding exercises with mentor feedback and language tracks. Great for improving problem-solving.
  https://exercism.org/
• Codewars — Fun, gamified coding challenges at many difficulty levels.
  https://www.codewars.com/
• LeetCode — Popular for algorithm/data structure practice. Free tier is useful even without premium.
  https://leetcode.com/
• HackerRank — Good for programming practice, especially if you want interview-style problems.
  https://www.hackerrank.com/

Best for beginner-friendly language learning

• W3Schools — Very approachable for quick explanations and in-browser examples, especially for web topics.
  https://www.w3schools.com/
• Python.org Tutorial — Official Python tutorial, clear and beginner-friendly.
  https://docs.python.org/3/tutorial/

If you like visual explanations

• Programiz — Easy-to-follow tutorials with examples and practice for several languages.
  https://www.programiz.com/
• Tutorialspoint — Broad coverage across many tech topics, with concise explanations.
  https://www.tutorialspoint.com/

Best picks by goal

• Absolute beginner: freeCodeCamp, W3Schools, Python.org Tutorial
• Web development: MDN, The Odin Project, freeCodeCamp
• Computer science concepts: CS50, GeeksforGeeks
• Practice problems: Exercism, Codewars, LeetCode, HackerRank

If you want, I can also give you:

1. a ranked list for beginners,
2. the best sites by language (Python, JavaScript, Java, etc.), or
3. a free study path combining these resources.