Using coding practice
How the in-browser runner and tests work.
- Run real code against real test cases without installing anything
- Earn XP and build a practice history with every passing challenge
- Get AI review of your code for style and correctness feedback
Run code in your browser
Open a challenge, write your solution in the editor, and hit Run tests. JavaScript/TypeScript run in a sandboxed Web Worker; Python runs via Pyodide (WASM). Each test case shows red (fail) or green (pass).
Submitting
When you're happy, Submit your solution. Passing challenges earns XP and contributes to your practice history. You can also ask for an AI review of your code for feedback on style and correctness.
Tips
- Read the prompt carefully — note the function name (
entry) the tests call. - Handle edge cases (empty input, large input, negatives).
- If Python won't load, use a JS/TS challenge — the runtime is downloaded on demand.
The journey, step by step
| Step | What you do | What you get |
|---|---|---|
| Open a challenge | Pick a challenge and read the prompt carefully | You know the function the tests will call and the edge cases to handle |
| Write & run | Write your solution in the editor and hit Run tests | Each test case shows red (fail) or green (pass), instantly, in-browser |
| Submit | Submit when all tests pass | XP earned and the challenge added to your practice history |
| Ask for AI review | Request an AI review of your solution | Feedback on style and correctness to level up your next attempt |
Frequently asked
Which languages can I practice in?
JavaScript and TypeScript run in a sandboxed Web Worker; Python runs via Pyodide (WebAssembly). Everything executes in your browser.
Why won't Python load?
The Python runtime is downloaded on demand and can take a moment on slow connections. If it won't load, switch to a JS/TS challenge and come back.
Do I earn anything for passing challenges?
Yes — passing challenges earns XP and contributes to your practice history, which feeds your competency record.