I built a web app that lets you seal a prediction, hypothesis, or decision with HMAC-SHA256 and anchor the proof to the Bitcoin blockchain via OpenTimestamps. The secret key never leaves your browser. The problem: Screenshots can be faked. Timestamps on centralized platforms can be disputed. There’s no trustless way to prove you said something before an outcome without relying on a third party. How it works: ∙ You write a message and generate a commitment locally in the browser ∙ The MAC gets anchored to Bitcoin via OpenTimestamps (~2 hour confirmation) ∙ You get a .psc file and a .ots file — the proof is in those files, not on my server ∙ When you’re ready, reveal your message and key — anyone can verify the math independently Use cases: Research pre-registration, prediction tracking, sealed decisions before negotiations, scientific hypothesis registration. What it doesn’t do: No anonymity, no forward secrecy, no message recovery if you lose your key. Live: psicommit.com Code: github.com/RayanOgh/psi-commit (MIT licensed) Happy to discuss the construction or threat model.