A blank Python tab.

Most online Python compilers ship your code to a sandbox on someone else’s server — which means signup walls, rate limits, and a 2-second cold start every time you hit Run. PyRun’s playground uses Pyodide, a full CPython build compiled to WebAssembly, so Python runs inside your browser tab. No account, no queue, no data leaves your machine. numpy, pandas, matplotlib, and requests are pre-installed and cached after first load — meaning the second visit works fully offline on a flight or a patchy hostel wifi. It’s not a toy REPL for print("hello"); it’s the same interpreter you’d use to prototype a real notebook, minus the Jupyter install.