JavaScript Runner

A full playground is the right tool for building something. A runner is the right tool for checking something: a reduce that looks wrong, a date format you never remember, a regular expression you want to try against a string. Paste, glance at the console, move on.

The runner executes inside a sandboxed iframe, which keeps it away from the rest of the page. That limits damage, but it does not make hostile code harmless — treat unfamiliar scripts with the same caution you would anywhere else, and never paste secrets into a snippet you are about to execute.

The sandbox allows scripts, but cross-origin network access still depends on the remote host and the browser. Prefer self-contained snippets that log values rather than calling APIs you do not control.

If your code runs without calling console.log (or warn/error), the runner reports that it finished successfully with nothing logged. Add a console.log to see values.

No. Everything runs in your browser as JavaScript — your code is never uploaded, never logged, and never sent to a server. You can verify that by watching the Network tab in devtools while you work, or by disconnecting from the internet after the page loads and confirming the tools still function. Nothing you paste is executed either; it is only ever parsed as text.