Paste a GST number and this checks its structure and its checksum digit, then tells you the state it belongs to and the PAN it contains. A mistyped GSTIN on an invoice is one of the most common reasons a buyer cannot claim input credit — and one of the easiest things to catch before the invoice leaves your desk.
A GSTIN is not random. Reading 27AAACB2345F1Z8 from the left:
That checksum is what makes real validation possible offline: a single mistyped character almost always breaks it.
This checks the format. It proves the number is well-formed and internally consistent, which catches typos, transposed characters and invented numbers.
It cannot tell you whether the registration is currently active, who it belongs to, or whether it has been cancelled — that lives on the GST portal's own search, and no offline tool can know it. Use this as the first filter, and the portal for the final word on a large or first-time customer.
Your invoice feeds your GSTR-1, which feeds your buyer's GSTR-2B. If the GSTIN on the invoice is wrong, the entry lands against somebody else's number or nobody's at all, and your buyer's input tax credit does not appear. They will notice at the end of the month, ask you to amend it, and the fix means editing a filed return.
Checking at the point of entry takes two seconds and avoids all of it.
The habit worth building is to validate a GSTIN once, when you first add the customer, and then bill from the saved record rather than retyping it. Most wrong numbers on invoices are not wrong in the customer master at all; they are typed fresh each month and mistyped on one of them.
Not from a format checker. Structure and checksum can be verified offline, but active-or-cancelled status only exists on the government GST portal.
It is the entity number — how many registrations that PAN holds in that state. The first is 1, the second 2, and so on through 9 then A to Z.
Almost always a transposed or mistyped character: the checksum is calculated from the other fourteen, so one wrong letter breaks it. Check the PAN section first, which is where most errors are.
No, but it contains one. Characters 3 to 12 of a GSTIN are the holder's PAN, which is why the same business has a different GSTIN in every state it registers in.