Check a stamp
Paste a stamp. Your computer checks if we really made it.Paste a stamp. Your browser checks that we signed it and that it is in our public log. It says VALID or FAKE.Paste the stamp JSON. Your browser verifies the Ed25519 signature over "HHH-STAMP-v1\nhash\nlabel\ndate\n" with our published key, then looks the stamp up in the append-only log. Signed but not logged reads FAKE.
The check runs on your computer. We do not see what you paste.The check runs in your browser; nothing you paste is sent to us. The date in a stamp is what we signed, not a clock anyone else checked.Runs client-side with WebCrypto; only the key and log are fetched. The signed date is our claim; only the OpenTimestamps anchor in /stamp.json proves when.
What is free, and what you pay for
Reading is free. Using our facts is free. You only pay if you want us to check your own work and give you a stamp that says so.Free to read, free to use: every fact, every proof, the map, the book, the checker and the AI tools cost nothing. You pay only for a stamp (our signed record that a machine checked something of yours) or a check (we run the machine check for you). Paying never changes what a fact says or how it is labeled.Free: every page, facts.json, the Lean proofs, the browser checker and the read-only MCP server. Paid (not on sale yet): a stamp, an Ed25519 signature over your hash, label and date, appended to the public hash-chained log; and a check, a machine check we run on your input. Labels come only from the checkers; money never touches them.