A timestamp answers one question with certainty: did this exact file exist at this moment? Put the answer on a public record and you can settle a lot of arguments before they start. Who wrote the draft. Which version of the contract went out. Whether your design existed before theirs.
People have improvised answers to this for a century: sealed envelopes, notary visits, emails to themselves. Today the honest comparison is short. You can get a stronger record than any of those, free, in the time it takes to drag a file across your screen.
What a timestamp does (and doesn't) prove
A timestamp proves possession: you had this exact file at this moment in time. That is real evidence, and it is often exactly what a dispute turns on. It is not proof of authorship truth, and it is not a legal copyright registration. Someone could timestamp a file they didn't create. What they can't do is timestamp it before you did, which is why stamping early, ideally the moment the work exists, is the whole game. There's more on the legal side in our guide to proving you made something first.
Timestamp a file in three steps
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Drop your file
Go to the drop zone on the Mark homepage and drop any file: a photo, a PDF, a song, a spreadsheet. Your browser computes the file's fingerprint (a SHA-256 hash) locally. The file itself is never uploaded.
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Get your proof link
A few seconds later you have a permanent link to a public record: this fingerprint, stamped at this time. The record is signed immediately (Ed25519) and joins a daily batch anchored to Arweave, a public record outside Tatastu's control (Base anchoring is optional). Copy the link somewhere safe, and keep the file: the file itself is the key.
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Verify anytime
Anyone can drop the file at makemark.io/verify and see the match: same fingerprint, same date. Verification is free forever, no account needed.
That's the whole flow. The browser drop zone needs no signup and no card. If you want to stamp from code instead, an API key includes one lifetime sample, and signed-in Mark accounts get 100 stamps each month. Details are in the API docs.
What's actually happening under the hood
The fingerprint is a SHA-256 hash: a 64-character string computed from your file's exact bytes. Change a single character in the file and the fingerprint changes completely. Two different files producing the same fingerprint is considered computationally infeasible, which is why the same technique protects things like software downloads and bank infrastructure.
Because only the fingerprint leaves your device, you can timestamp private things: an unpublished manuscript, a term sheet, an invention disclosure. Nobody can read your file from its fingerprint. You reveal the content only if and when you choose to.
Durability is the other half. Once the daily batch is anchored, your record lives on Arweave, with Base supported as an optional additional witness. Download the bundle to check its signed receipt and Merkle path offline with the MIT-licensed verifier on npm. Keep it with the original file so those checks do not depend on Mark. Independently checking the public anchor requires ledger access.
The other ways people timestamp files
Being fair about the alternatives: each of these still exists because it once solved the problem, and one of them still has a place.
Mailing or emailing it to yourself
The classic "poor man's copyright." It's free and easy, and that's where the good news ends. Envelopes can be unsealed and resealed, postmarks date the envelope rather than its contents, and email dates depend entirely on your provider's records. Courts give it very little weight. Since a cryptographic timestamp is just as free and far stronger, there's no longer a situation where this makes sense.
A notary
A licensed human verifies your identity and witnesses a signature. That carries real legal weight, and some processes (affidavits, property deeds) explicitly require it. But it costs money per document, takes an appointment, and attests to what the notary saw on paper, not to the exact bytes of a digital file. Use a notary when the law asks for one, not for everyday "I had this first" evidence.
Blockchain timestamping services
These put your file's fingerprint on a public blockchain, which makes backdating practically impossible. OpenTimestamps does this for free against Bitcoin but expects you to run client software and keep a proof file. Commercial services like OriginStamp wrap it in an API and paid plans. Strong evidence either way; the difference is friction and cost. We compare them properly in blockchain timestamping options, compared.
| Method | Cost | Time | Strength as evidence |
|---|---|---|---|
| Email to self | Free | A minute | Weak: dates are easy to dispute |
| Notary | Fee per document | An appointment | Strong for signatures; doesn't bind digital bytes |
| OpenTimestamps | Free | Setup, then fast | Strong: anchored to Bitcoin |
| Mark drop zone | Free | About 30 seconds | Strong: signed now, anchored to Arweave (Base anchoring is optional) |
One more habit worth building: once you've stamped something, you can check it, and so can anyone you send it to. Our guide on checking whether a file is authentic covers what a match, a conflict, or no record actually means.
Common questions
Is timestamping a file really free?
Yes. Every durable Mark account gets one lifetime sample stamp with no card, and signed-in accounts get 100 per month. Prepaid packs start at $1. Verifying any stamp is free forever, for anyone. See pricing for the details.
Does my file get uploaded?
No. Your browser computes the file's SHA-256 fingerprint locally and only that 64-character fingerprint is sent. Nobody can reconstruct your file from the fingerprint, so you can safely timestamp private work.
Is a timestamp legally binding?
A timestamp is evidence, not a registration. It proves you had this exact file at a specific moment. It does not prove authorship truth and it is not a legal copyright registration. This is not legal advice; for a specific dispute, talk to a lawyer.
What happens to my timestamp if Tatastu shuts down?
The record is anchored to Arweave, a public record outside Tatastu's control (Base anchoring is optional). Keep the original file and download the bundle after anchoring. Its signature and Merkle path can be checked offline; independently checking the public anchor requires ledger access.