myDATA MARK
Validator
Validate the structure, format, and pairing of Greek myDATA MARK numbers and UID hashes — entirely in your browser, with nothing sent to a server.
About Greek myDATA MARK Validation
The validator checks conformity with Greek standards: 14 to 16-digit numeric MARK numbers, 40-character lowercase hexadecimal SHA-1 UID hashes, and paired UID/MARK records.
Privacy protection: validation is executed entirely in-memory on the client without sending sensitive information to external servers.
myDATA Validation Algorithm
| Step | Description |
|---|---|
| 1. Detect the format | Detect whether the input is a single MARK number (14–16 digits), a single UID hash (40 hex characters), or a paired record in the form "UID: [hash] MARK: [number]". |
| 2. Check the characters and boundaries | Verify hex character validity and the numeric boundary conditions for the MARK protocol. |
| 3. Return the decoded result | Return structured decoded elements for a detailed compliance audit. |
Frequently Asked Questions & Technical Guidelines
What are the consequences of MARK rejection in Greece?
An invoice that AADE rejects — or that was never assigned a MARK — is not considered properly transmitted to myDATA, which can affect VAT return pre-filling, expense deductibility for the recipient, and compliance audits. Businesses are expected to detect and correct transmission failures and resend rejected invoices.
Does this tool confirm a MARK or UID is real and registered with AADE?
No. This tool only checks structural format (digit/hex-character counts and pairing) — it cannot confirm a MARK number was actually issued by AADE or that a UID corresponds to a real transmitted invoice, since that requires checking AADE's own records. Nothing is sent to a server; all checks run locally in your browser.