Free vs Paid Document Timestamping
Free blockchain timestamping is not a trick. Services like OpenTimestamps really are free and really do work, because they batch thousands of hashes into one transaction. The honest question is not whether free works, but what you are taking on when you use it.
Why free is possible
An on-chain transaction costs money, so a service writing one per customer must charge. Free services avoid that with Merkle aggregation: collect many hashes, combine them into a tree, and publish only the root. One transaction covers everyone in that window, and the cost per timestamp rounds to nothing.
The cryptography is entirely sound. Your proof shows your hash is in the tree, and the tree root is on-chain.
What you take on instead
The cost does not disappear; it moves to you.
You must keep a proof file. With aggregation, the chain holds a Merkle root, not your hash. The file linking the two — an .ots file, typically — is the proof. Lose it and the timestamp is unrecoverable, because nothing on-chain points at your document.
There is a step you can forget. Aggregated proofs are incomplete until the batch confirms and you run an upgrade. People submit, feel protected, and never upgrade. The failure is silent and only surfaces when it matters.
The artefact is technical. You get a binary file, not a document. Explaining Merkle aggregation to a court, a client or an insurer is your job.
Nobody is accountable. Free means community support and no obligations. Fine for most uses, uncomfortable for a dispute.
Retention is a promise, not a contract. Calendar servers are run by volunteers. They have been reliable for years, and they owe you nothing.
What paid services add
Not better cryptography — the hash and the chain are identical. What you buy is the operational layer:
- A direct transaction. Your hash goes into its own transaction, readable on a block explorer with no proof file and no client software.
- A self-contained certificate. A readable document with the hash, the transaction, the payload and a verification link — something you can hand over.
- No step to forget. Confirmed is confirmed.
- Nothing to lose. If you mislay the certificate, the transaction is still public and still contains your hash.
- Someone to ask. A support channel and an actual counterparty.
Which to choose
Free is the right call when you are technical and will genuinely manage proof files; you are timestamping in volume where per-item cost dominates; you are integrating into software you control; or the stakes are moderate and a lost proof would be annoying rather than serious.
Paid earns its fee when the document could end up in a dispute; a non-technical third party may need to verify it; you want an artefact rather than a workflow; you are doing this occasionally, so per-item cost is irrelevant; or you would simply rather not carry the operational burden.
The cost comparison people actually care about
Set against the alternatives, both are cheap. US copyright registration runs to tens of dollars per work and takes months. A notary charges per document and per page. An hour of a lawyer's time exceeds a lifetime of timestamps.
So the free-versus-paid question is rarely about money. It is about whether you want to own the operational burden or hand it off — a few dollars either way.
What neither one gives you
Worth repeating, because both free and paid services get marketed loosely:
- Neither proves authorship. Both prove existence and integrity at a time. See proof of existence vs proof of authorship.
- Neither is a registration. Copyright registration is a separate legal act with separate benefits.
- Neither protects a file you then lose or modify. The record is only as useful as the original you keep beside it.
If a service claims otherwise at any price, that is the signal to walk away.