Test Safely in DevTools
Before saving anything as a bookmark, paste the code in DevTools console on a non-sensitive page and observe the output carefully. Log intermediate steps, handle null cases gracefully, and undo any mutations if something surprises you. Maintain a scratchpad page, too, for quick trial and error. When the code behaves reliably there, elevating it into a bookmarklet becomes a confident, controlled move rather than a risky experiment.