Interactive demo · try it yourself
How a typo gets caught
When you copy down twelve seed words, one nagging fear is: what if I write one down wrong? Those words carry a built-in safety net called a checksum, and most of the time it catches exactly that — a proper wallet refuses the whole phrase before a single coin is at risk. Generate a throwaway seed and try to slip a typo past it. Then read the part underneath the demo, because "most of the time" is doing real work in that sentence.
The seed below is randomly generated in your browser and thrown away when you leave. Never type your own seed words into any website. There's no free text box here, on purpose.
Make a valid throwaway seed, then tap a word to "miscopy" it.
Runs entirely in your browser · nothing is sent, saved, or logged.
Tap any word to introduce a typo — tap it again to fix it:
To make the point cleanly, this page always swaps in a word that breaks the maths. Real
miscopying is not so obliging. Roughly one wrong phrase in sixteen still adds up —
the checksum passes, no error appears at all, and a real, perfectly ordinary,
empty wallet opens instead of yours. Nothing tells you it is the wrong one.
That is why a phrase being accepted is not proof your backup works. The only proof is
restoring from it — wiping a device and bringing the wallet back from your written words — before you trust it with
anything. It is a lesson of its own later in the course.
The last word isn't random — it packs a checksum: a few bits computed from all the other words (you saw this in how a seed is born). Change a word and that math usually no longer adds up, so the wallet knows something's off and stops you before you rely on a broken backup.
✓ Last verified: August 4, 2026