The Sealed Bet
Write down a prediction, a bet or an answer now. This page turns it into a short seal code you can post anywhere people will see it. Later, you reveal the words and anyone can check them against the code. Nobody can learn the words from the code, and nobody, you included, can change a word afterwards and still match it.
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Every character counts, spaces and line breaks included. Write it the way you will want to read it out later.
SEAL
Seal code (post this, with today's date, somewhere other people or a server will timestamp it)
Keep these two things private until the reveal, and keep them together:
the exact words above, and this key:
Lose either and the seal can never be opened, by anyone. Paper works.
How it works, plainly
The seal code is the SHA-256 fingerprint of your key followed by your words. Change one letter of the words, or use a different key, and the fingerprint changes completely. Going backwards, from fingerprint to words, is not practical for anyone.
Why the key exists. Without it, a short bet like "yes" or "the Lions" could be found by trying every likely answer until one matched the code. The random key makes that hopeless, which is also why it must be kept private until the reveal.
What it cannot prove. When you sealed it. This page has no clock anyone else trusts. The date comes from wherever you post the code: an email to yourself and a friend, a group chat, a public post. Post it before the outcome is known, somewhere you cannot quietly edit.
The honest edge. A seal proves what was written, not that it was the only thing written. Someone could seal ten different guesses and reveal the lucky one. If that matters, post every code you make, or let the other side see you post exactly one.
Everything happens in your browser. Nothing is sent or stored anywhere; close the tab and it is gone, so copy what you need.