GSTIN and PAN validation

Villva validates GSTIN and PAN as you type them, so a malformed tax identifier is caught before it can break an invoice, e-invoice (IRN), e-way bill or GST return.

GSTIN validation

A GSTIN is 15 characters: a 2-digit state code, a 10-character PAN, an entity digit, the letter Z, and a final check digit. Villva checks all of the following:

The full 15-character structure
A valid 2-digit state code
The PAN embedded inside the GSTIN
The final check digit (worked out with the official calculation, not just the length)

Examples:

Input	Result
`33ABCDE1234F1Z5`	Accepted
`33ABCDE1234F1Z9`	Rejected, bad check digit
`99ABCDE1234F1Z5`	Rejected, invalid state code
`33ABCDE1234F1Z`	Rejected, wrong length
`33abcde1234f1z5`	Rejected, wrong case/format

PAN validation

A PAN follows the pattern of 5 letters, then 4 digits, then 1 letter. ABCDE1234F is accepted; ABCD1234FG is rejected because it does not match that pattern.

Place of supply

The state code embedded in a GSTIN identifies the supplier or buyer state. Villva reads that state code and uses it to decide the place of supply, which in turn decides how tax is applied:

Same state (intra-state): tax is split as CGST + SGST.
Different states (inter-state): tax is charged as IGST.

So a correct GSTIN is not just a formatting nicety: it directly drives whether an invoice carries CGST + SGST or IGST.

When and where it applies

Validation runs as you type and is then checked again authoritatively when you save. The check when you save is the one that counts, so skipping past the on-screen warning does not let a bad identifier through.
An invalid GSTIN or PAN is rejected with a specific message and blocks the record from being used to generate an IRN, generate an e-way bill, or file a GST return until you correct it.
Customer and vendor masters store the GSTIN that this validation checks, so the place-of-supply decision on every document raised for that party stays correct.