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Prove your file existed — right now

Upload any file and get a cryptographic timestamp anchored to the Bitcoin blockchain. Your file never leaves your browser — only its 32-byte hash is sent to OpenTimestamps calendar servers. Free, open standard, verifiable forever.

Drag & drop files here

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File upload

Your files never leave your browser · No account required · Free forever

Why use this timestamper?

Files stay on your device

Your files are hashed locally in the browser — only a 32-byte fingerprint is ever sent to the network. Not a single byte of your document touches our servers.

Bitcoin-anchored proof

Each timestamp is committed to the Bitcoin blockchain, the most tamper-resistant ledger on earth. Your proof will still be verifiable decades from now.

Any file, any size

PDFs, images, source code, spreadsheets, videos — it doesn't matter. Because we hash the file, size is irrelevant and no format is off-limits.

Batch multiple files at once

Drop a whole folder at once. Multiple files are aggregated into a single Merkle tree, so stamping ten files takes the same time as stamping one.

Open, verifiable standard

The .ots files you download are an open standard. Verify them any time with the official OpenTimestamps client, any compatible tool, or directly against a Bitcoin node — no dependency on us.

Done in seconds

Hashing happens instantly in your browser. The calendar round-trip typically takes 2–5 seconds. You'll have your proof file before you've had time to second-guess it.

Why you might need to timestamp a file

A contract signed before the deadline

You're a freelancer and you've just finished a proposal. The client's brief asked for submissions before midnight — you hit send at 11:58, but two days later they claim it arrived late. You wish you had proof.

Next time you draft a proposal, you drop the final PDF into the timestamper before sending it. In three seconds you have a .ots file that cryptographically proves the document existed at that exact moment. If there's ever a dispute, you open your timestamp file and the blockchain record speaks for itself — no arguing with math.

It doesn't matter whether you're dealing with a client, a court, or an insurance company. A Bitcoin-anchored timestamp is independently verifiable by anyone, with no middleman who could lose records or go out of business.

Protecting original creative work

You've spent three months writing a novel. You've heard horror stories about writers who couldn't prove their manuscript predated a plagiarism claim. Copyright registration exists, but it's slow, costs money, and requires you to trust a single institution.

You drag the manuscript file onto the timestamper. Ten seconds later, you have a .ots proof file sitting next to your draft. You do the same thing every time you finish a meaningful revision.

If someone ever claims your work as theirs, you have a chain of dated proofs anchored to the Bitcoin blockchain — one of the most audited, tamper-resistant records in existence. You didn't need a lawyer, a notary, or a subscription. Just a browser and a few seconds.

1

Select your files

Drop any file — or several — onto the uploader. PDFs, images, source code, anything goes.

2

We hash and stamp

Your files are hashed in your browser, then the fingerprints are submitted to OpenTimestamps calendar servers and committed to the Bitcoin blockchain.

3

Download your proof

You get one .ots file per input file. Keep it alongside your original — together they're your timestamp proof, verifiable at any time.

  • Your files never leave your browser — there's nothing to delete.
  • We never see, store, or share your files. Only a 32-byte hash touches the network.
  • No sign-up, no email, no account. Just upload and timestamp.