I built a tool that lets you seal a prediction, hypothesis, or decision and prove you made it before the outcome without trusting any third party. The problem is that there is no simple trustless way to prove you knew something before it happened. Screenshots get faked, centralized timestamps get disputed, and you always end up asking someone to trust your word. The construction: your message is locked with HMAC-SHA256 and a 32 byte secret key generated by window.crypto.getRandomValues in the browser. The key never leaves your device. We store only the MAC. A canonical stamp file containing the commitment ID, MAC, and timestamp is SHA256 hashed and submitted to OpenTimestamps calendar servers. The resulting OTS receipt anchors the commitment to a real Bitcoin block. What it provides: cryptographic binding, cryptographic hiding, Bitcoin timestamp via OpenTimestamps, domain separation to prevent replay attacks, and constant time comparison to prevent timing attacks. What it does not provide: anonymity, forward secrecy, or message recovery if you lose your key.