Notarize a file. Keep the file.

Anchor a tamper-evident proof of any file to the Bitcoin SV blockchain in seconds. Your file is hashed locally in your browser; only the hash leaves your device. Get back a printable receipt + an offline-verifiable bundle anyone can re-check against the chain.

Want to see a real receipt before submitting your own?

We've notarized a small public file as a demo. Open the receipt page, download the bundle, and re-verify it on the verifier against the live chain.

View demo receipt Download demo bundle View tx on WhatsOnChain

Notarize

Private receipt — file never leaves your device

Your browser computes the SHA-256 hash locally; only the hash, file size, and any optional label you provide are sent to the server. Best for confidential material: legal documents, client work, internal evidence, source protection.

Shareable evidence bundle — includes a copy of the file

The file is uploaded and packaged into the receipt bundle so anyone you share the bundle with can re-verify the original against the chain. Best for portability, audit trails, third-party submissions. Max upload size: 1 MB.

File

Drop or pick a file…

Filename label (optional — stored in your local bundle manifest only, never on chain) Memo (optional — local manifest only, not on chain)

✓ Your file will not be uploaded. Hashing happens entirely in your browser. Only the SHA-256 hash, file size, and any label you typed above will be transmitted.

How verification works

Open the verifier in any browser. It runs entirely client-side; nothing uploads.
Drop your .mbnt bundle on it. The verifier re-canonicalizes the receipt JSON, hashes it with WebCrypto, and compares to the on-chain MBNT OP_RETURN.
If you kept the file private, also drop the original file on the page — it hashes locally and compares to the committed SHA-256.

Privacy & Trust

Does my file leave my computer?

In Private receipt mode (the default): no. Your browser computes the SHA-256 hash locally using the WebCrypto API. Only the hash, file size, and any optional label you typed are transmitted — never the file's bytes.

In Shareable evidence bundle mode: yes, the file is uploaded so it can be packaged into the bundle. Use this mode only when you want a portable proof anyone can re-verify, and don't mind the file transiting our server.

What gets stored on the BSV blockchain?

A 34-byte OP_RETURN output containing:

The 4-byte magic MBNT + 1 byte version + 1 byte subtype
A 20-byte document_hash = SHA-256 of the canonical receipt document, truncated
A few small TLV fields (issuer ID, timestamp)

The canonical receipt document itself contains your file's SHA-256 and byte count — nothing else from your submission.

Is my filename or memo visible on the chain?

No. Filename labels and memos are stored only in the local .mbnt bundle manifest, never in the canonical document that gets hashed for the on-chain receipt. They are intentionally excluded so a sensitive filename like internal-investigation.pdf can never appear in any public record.

What happens if you (the operator) get hacked?

The signing wallet's xprv lives in the server's process memory. A successful breach could drain that wallet (currently capped at a small float of sats — see fee cap and rate limit settings). Your private receipts are unaffected: your file never reached us, so there is nothing of yours to steal. Past on-chain receipts are immutable and cannot be revoked.

How do I verify a receipt myself, without trusting you?

Open the verifier in any modern browser (Chrome, Firefox, Safari). Drag your .mbnt bundle onto the page. The verifier:

Re-canonicalizes canonical.json using WebCrypto and compares the hash to doc_hash_expected in the manifest;
Fetches the on-chain transaction from a public BSV node (whatsonchain.com) and compares the on-chain document_hash to (1);
If you also drop your original file on the page, hashes it locally and compares to subject.document_sha256.

The verifier runs entirely in your browser. Nothing is uploaded. The same HTML file works offline (download verifier.html from /verify).

What does it cost?

Free preview. Currently rate-limited to 1 submission per IP per hour, max file size 1 MB, hard fee cap of 50 sats per receipt. The operator pays the BSV network fee (~25 sats) out of a shared demo wallet.

Why BSV and not Bitcoin (BTC) or Ethereum?

BSV's miner fee policy makes OP_RETURN data outputs cheap (~$0.0001 per receipt at typical exchange rates), and the payload size budget is generous. The same MBNT scheme could run on other chains; the choice here is operational, not philosophical.

Data retention

What we keep

Your bundle (manifest.json + canonical.json; in shareable mode, also your file) on the operator host, addressable at /bundle/<id>.mbnt. Anyone with the bundle ID URL can download it. Delete on request.
The bundle ID in URLs we produce. The URL is the only handle we expose; we don't index by IP, filename, or hash.
HTTP access logs (Caddy reverse proxy): one JSON line per request with timestamp, source IP, path, status. Rotated by Caddy.

What we don't keep

Your file's bytes in private mode — they never arrive.
Filename or memo on the BSV chain — they live only in the local bundle manifest.
Per-IP rate-limit counters survive only until the next service restart (in-memory).
The signing wallet's xprv — it's loaded into process memory at start, never written to disk.

The on-chain receipt is permanent

Once broadcast, the MBNT receipt sits in the BSV ledger forever and cannot be deleted by anyone, including us. It contains nothing personally identifying — just a 20-byte hash and a few small metadata bytes. If you need a receipt removed from the operator host, ask — we'll delete the bundle, but the on-chain commitment will remain (and that's a feature: it's what makes the proof tamper-evident).