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How to timestamp text to the Bitcoin blockchain, free

A blockchain timestamp is a public, tamper-proof receipt that some text existed at a certain moment, like a notary stamp, but backed by Bitcoin instead of a person. Here is how to create one in seconds, for free, and verify it yourself later.

Last updated June 2026

What a blockchain timestamp actually is

A timestamp proves a piece of text existed before a point in time. Done on Bitcoin, that proof needs no trusted third party: no notary, no company, no server you have to believe. It is sometimes called a proof of existence.

Crucially, your text is never uploaded. The tool computes a SHA-256 hash, a short fingerprint of your words, and only that fingerprint is anchored to the blockchain. The text stays yours until you choose to reveal it.

Why Bitcoin, and why it's free

Bitcoin is the most expensive ledger in the world to rewrite, which is exactly what makes a timestamp anchored to it credible: moving or forging that timestamp would mean rewriting Bitcoin itself.

The free part comes from OpenTimestamps, an open standard that batches thousands of hashes into one Bitcoin transaction through public calendar servers. You get Bitcoin-grade proof at effectively zero cost, with no account and no wallet.

How to timestamp text to Bitcoin, step by step

  • Write or paste your text. A prediction, a claim, an idea, or any statement you want to lock to a moment in time.
  • Stamp it. The tool hashes your text locally and anchors the hash to Bitcoin through OpenTimestamps. This takes seconds.
  • Keep the proof. Copy the verify link or download the .ots proof file. The Bitcoin attestation finalizes within a few hours.

The fastest way to do this for text is Sentari's Proof of Call, which is built for stamping statements and predictions rather than files.

How to verify a timestamp later

Verification recomputes the hash from the original text and checks it against the Bitcoin attestation in the proof. You can do it on the verify page, or independently with the standard open-source ots tool, so the proof never depends on any one website staying online.

What people use it for

  • Predictions: prove you called a market move, a score, or an outcome before it happened.
  • Ideas and authorship: timestamp a concept, draft, or design before you share it.
  • Records and agreements: prove a document or message existed on a given date.

For the prediction use case specifically, see how to prove you called a crypto trade.

Frequently asked questions

Is blockchain timestamping free?
Yes. OpenTimestamps anchors to Bitcoin through public calendar servers that need no account or API key. They batch many timestamps into a single Bitcoin transaction, so the cost of one stamp is effectively zero.
How does timestamping text to Bitcoin work?
Your text is run through a SHA-256 hash, a short fingerprint that reveals nothing about the content. Only that hash is anchored to a Bitcoin block, creating mathematical proof the text existed before the block was mined. The text itself is never published.
Does my text get published on the blockchain?
No. Only the hash is anchored. Your actual words stay private unless you choose to reveal them. To verify later, you provide the original text and the proof, and the hash is recomputed and checked against Bitcoin.
How do I verify an OpenTimestamps (.ots) proof?
Use Sentari's verify page, or drag the .ots file and the original text onto opentimestamps.org, or run the open-source ots tool locally. All three check the proof against Bitcoin without trusting any single company.
When is the timestamp confirmed?
The commitment is recorded instantly with the calendar, and the Bitcoin attestation typically lands within a few hours. After that, the proof is permanent and verifiable forever.

Sentari provides software and information, not financial advice. Crypto trading involves risk, including the loss of capital. Past performance is not a guarantee of future results.