IndentationError, a missing colon or an unclosed bracket stop a Python program before it starts. This checker points to them instantly as you type, explains common beginner mistakes (= instead of ==, print without brackets, else if, ++, a list as a default argument) and, with one tap, compiles the code with real Python 3.12 running in your browser.
loading toolHow to use the python checker
- Paste your code into the box (or tap Try a sample).
- Read the list of problems: ✕ marks an error, ! a warning.
- Tap Show next to a problem to jump to that line, fix it, and watch the list update.
Good to know
- Use 4 spaces for each indent level and never mix tabs and spaces.
- Every if, for, while, def and class line ends with a colon.
- Compare with None using “is None”, not “== None”.
Questions
What does “Check with real Python” do?
It loads Pyodide, the official Python compiled for the browser, and asks Python itself to compile your code. Any syntax error it reports is exactly what you would see on your computer.
Does it run my program?
No, it only checks it. To run Python, use the Run Python tool.
Does my code get uploaded?
No. The checker or runtime is downloaded once from a public CDN (jsDelivr or cdnjs) and then runs inside your browser. Your code never leaves your device.
Is my data private?
Yes. Everything happens inside your own browser: nothing you type or choose is uploaded to us or anyone else.
Is it free?
Completely free, with no sign-up, no watermark and no limit on how many times you use it. Light ads keep the site running.
