The free OpenTimestamps tool,
or a paid API?

The short answer

OpenTimestamps (opentimestamps.org) is the open protocol this service is built on. Its website stamps and verifies files in your browser, for free, with no account. The command-line clients do the same for scripts. What it does not provide is a batch API, a callback, a receipt, or anyone to call when something breaks — and that operational layer is what $0.05 a hash buys here.

If you stamp one document a month, use the free tool. We would rather you did than pay us for something you do not need.

What the free tool does well

• It is free, and the public calendars (Alice, Bob, Finney, Catallaxy) run on donations with no registration or API key.
• It hashes in your browser: the file never leaves your machine, same as here.
• It is the reference implementation of the standard, in Python, JavaScript and Java, so ots stamp and ots verify work on any .ots file.
• It verifies without trusting anyone, given a Bitcoin node: the proof is replayed from your hash to a block header you check yourself.
• It is honest about the format: the .ots file is the product, and no service can withhold it from you.

Where the free tool stops

• One file at a time in the browser, with a download per file. A pipeline with a thousand outputs needs a loop, a store and a retry policy, which is exactly the code you would be writing.
• Installing software for the CLI: Python, Node or Java, plus a cron or a worker to run it. On a locked-down build agent, that is a ticket.
• ots verify needs a Bitcoin node to check a complete proof locally. Without one, you are back to uploading files to a website, by hand.
• No batching, no webhook, no receipt. Nothing tells you when a proof completes, and nothing signs the fact that you submitted that hash at that time.
• No support. The calendars are volunteer-run; the maintainers owe you nothing, and that is fine until a production pipeline depends on it.
• No way to pay from software. Free is free, but an agent still needs someone to install and run the client, and that someone is a human.

Side by side

Why pay for something that is free?

You are not paying for the timestamp; you are paying for the call. $0.05 buys the submission to four calendars, the retry when one is down, the Merkle tree and the nonce that keeps your hash private inside a shared batch, the proof assembly, the upgrade when Bitcoin confirms, the signed receipt, the webhook, and a verify endpoint that finishes pending proofs. That is a few hundred lines of code and an on-call rota you do not have to own.

If you already have that code, keep it. The protocol is open and we are not going to pretend a paid wrapper is more secure than the thing it wraps. Our proofs are ordinary .ots files, and they do not need us to be true.

You can leave whenever

Every proof we issue is a standard OpenTimestamps file. Upload the file and its proof at opentimestamps.org and it verifies; run ots verify against your own node and it verifies. Once a proof is complete, it does not depend on this service, our database, or our continued existence. While a proof is still pending, it depends on the calendars that will commit it — which is true of the free tool too.

That is deliberate. A proof you can only check by asking the company that sold it is a weaker artifact than a file you can hand to a judge, a counterparty or a stranger with a node.

How to choose

1. Stamp once, by hand? Use opentimestamps.org. Free, private, done.
2. A script stamps a few files a day and you can run ots there? The CLI is fine; wrap it in a cron and keep the proofs.
3. A pipeline or an agent stamps at volume, and needs to know when proofs complete? Use the API: batches, webhooks, receipts and a verify call that upgrades pending proofs.
4. You need a batch of 100 in one payment, from a wallet, with no signup? That is this service.

Questions