Sandboxed execution
Python, C++, Java and JavaScript run inside an isolated container runner. Nothing touches the app runtime.
Write it, run it, understand its complexity.
CodeBlock is an online compiler and IDE for Python, C++, Java, JavaScript and SumoLang - with a custom test-case runner, an automatic Big-O profiler and a snippet library you can share with a short link. Draw your logic on the built-in whiteboard while you code, and let AI explain any error you hit.
Python 3C++ 17Java 17JavaScriptSumoLang
Everything in one panel
Time & space profiler
A rule-based static analyzer estimates both time and space Big-O from loop nesting, recursion, halving, sorts and allocations - with a pluggable analyzer interface.
Typing trainer
Practise touch-typing real code in all five languages - 10 drills each, with live WPM and accuracy so your fingers keep up with your ideas.
Test case runner
Feed stdin, set expected output and get a line-by-line pass/fail diff without leaving the editor.
SumoLang, by Sumedh Pimplikar
A custom language with a deliberately silly syntax - sumo instead of let, yeet instead of return, stomp instead of loop - with its own parser, interpreter and full syntax reference.
Snippet library
Save your programs to your account, reopen them in one click and keep working where you left off.
Whiteboard while you code
Sketch the algorithm next to the editor - multi-colour pens, eraser, erase-all, undo and redo - or open the full Whiteboard tab for shapes, a highlighter and PNG export.
AI error explanations
When a run fails, one click sends the error and your code to an AI tutor that explains it in plain English and suggests a fix.
Share links + expiry
Flip a snippet to public for a short share URL, with an optional expiry timestamp that kills the link automatically.
Save your work, share a link
Create a free account to keep a personal snippet library. Public snippets get a short URL, and you can set an expiry so the link stops working on its own.
Get started