1. Calculating the Data File Hash Value

Calculate the hash value associated to the data file to be timestamped; the hash value acts as a digital fingerprint, 'uniquely' identifying the unmodified original document.
The hash is calculated locally inside the browser without disclosing the document to third parties, preserving privacy; no internet connectivity is required.

2. Submitting the Hash for Attestation

Submit the hash to a selected set of OpenTimestamps public calendar servers (e.g. btc.ots.dgi.io) for attestation of its existence (timestamp) in the Bitcoin blockchain using a Bitcoin transaction; internet connectivity is required. The submission receipt is saved locally.
In time, this hash will be attested in a Bitcoin block header and the submission receipt will become upgradable to attestation proof. The submission receipt is not an attestation proof yet, i.e. it cannot be verified immediately: it is incomplete as it takes up to few hours for the timestamp to get confirmed by the Bitcoin blockchain.
To avoid the inefficiency of one blockchain transaction for every document hash, a calendar server provides aggregation of multiple hashes in a Merkle tree data structure and performs their attestation in a single transaction, effectively attesting only the Merkle tree root, which is itself a hash value.

3. Loading the OTS Receipt/Proof From File

Load an existing OTS receipt/proof from a local file; no internet connectivity required.

4. Displaying the OTS Receipt/Proof Informations

Display the informations included in the OTS receipt/proof, including the actual commitment operations and attestations (if any); no internet connectivity is required.

5. Upgrading the OTS Receipt/Proof

Attempt the upgrade of the OTS receipt/proof with attestations that might be available from the selected OpenTimestamps calendars; internet connectivity is required.
To be upgraded to proof status, incomplete receipts require the assistance of the remote calendars used for timestamping: each calendar has to provide its attestation as path to a Bitcoin block header. Upgrading an OTS receipt adds the path(s) to the Bitcoin block header(s), making it a self-contained calendar-independent OTS proof.
Even proofs can be updated, if there is a calendar that can add its own attestation to the ones previously provided by other calendars.

6. Verifying the OTS Receipt/Proof

Verify the attestations included in the OTS receipt/proof (if any); internet connectivity is required.
OTS receipt/proofs can be verified independently from any OpenTimestamps server or facility, using a local Bitcoin Core node; anyway, since a web-page cannot access the local filesystem, this page relies on public block-explorers for verification.
First an upgraded proof is obtained from the selected calendar servers if available (as in the step above, performed also here to ensure updated informations), then the receipt/proof status is displayed below.