Verifiable agreements, anchored in Bitcoin.
Every proof is anchored in Bitcoin and can be verified with independent tools, without relying on us. It may also carry an ML-DSA-87 (FIPS 204) co-signature produced on a machine that never touches the network, verifiable against the published X-39 fingerprint.
Two people or companies close a deal over a chat encrypted in the browser, both accept it, and a certificate with a Bitcoin timestamp remains.
Write or upload the agreement
Text or file. The SHA-256 hash is computed in your browser. For a file, only the hash and its name travel; if you type the text here, the text is sent to the service to enable the agreement and the evidence.
Agree and accept
A chat encrypted in the browser between the two parties. When both accept, the conversation freezes and its hash becomes part of the proof.
Sealed on Bitcoin
A public certificate anyone can verify, with no account and at no cost.
How it protects you
Anchored in Bitcoin
The agreement and the frozen chat are anchored to a Bitcoin block via OpenTimestamps. The proof shows the hash existed before that block, and you verify it without us.
Air-gapped ML-DSA-87 co-signature
Proofs may carry an ML-DSA-87 (FIPS 204) co-signature produced on a machine that never touches the network. It is verified against the published fingerprint of the X-39 COLD key, not only against the key included in the evidence. No operator signing key lives on any connected server: the historic WARM signature was retired in July 2026.
Verifiable by anyone
Free, no fees. Download the .ots proof and validate it with independent tools: no need to trust us.
Who it's for
Journalists, sources and human-rights organisations that need to prove a document existed — and what it said — before someone denies, seizes or deletes it, without relying on a platform that can be pressured or switched off. Also freelancers and clients, small businesses closing deals, and anyone who wants to date-stamp an idea or patent before sharing it.
Pricing
Free. No fees. We do not charge for creating, accepting, sealing or verifying. The code is free software (AGPL-3.0).
Verifiable honesty
We custody no funds and sell no tokens. Files are not uploaded: only their SHA-256 fingerprint travels. Text typed on the site is sent to the service. The "Confirmed" state only appears with a real Bitcoin block attestation.
See the code on GitHub →