GSTIN Validator & Checksum Verifier
Check whether an Indian GST number is genuine by verifying its official check digit, and see the state, the PAN inside it, and the type of business it belongs to. Runs entirely in your browser.
Last updated: 2026-08-31
Spaces, hyphens and lowercase are fine. Checked as you type ā nothing is sent anywhere.
ā Valid ā 27AAPFU0939F1ZV
| State | Maharashtra (code 27) |
| PAN of holder | AAPFU0939F |
| Holder type | Firm / Limited Liability Partnership |
| Registration number for this PAN in the state | 1 |
| Check character | V ā verified |
A valid check digit proves the number is well-formed. It does not prove the registration is currently active ā only the official GST portal can confirm that.
Key Features
- Real checksum verification: computes the official mod-36 check digit rather than only checking the shape.
- Tells you what is wrong: a mismatch reports the character it expected, so you can spot a typo.
- Decodes the number: state, embedded PAN, holder type and registration sequence.
- Instant: validates as you type, with no button to press.
- Private and offline: the arithmetic runs in your browser; the number is never transmitted.
How to Use This GSTIN Validator
- Paste or type the 15-character GST number into the box. Spaces and hyphens are ignored.
- The verdict appears immediately ā valid, or the specific reason it is not.
- If the check digit is wrong, compare the expected character shown against what you have; a single transposed pair is the usual cause.
- For a valid number, read the decoded state, PAN and holder type below the verdict.
How GSTIN Validation Actually Works
A GSTIN is 15 characters and each part carries meaning. The first two digits are the state code. The next ten are the PAN of the business, which itself encodes the holder type in its fourth character. The thirteenth is the registration sequence for that PAN within that state, the fourteenth is nearly always Z, and the fifteenth is a check digit.
That last character is what makes real validation possible. It is computed from the other fourteen: each character takes a value from 0 to 35, alternate positions are weighted by one and two, each product is reduced by adding its quotient and remainder against 36, and the check character is whatever makes the running total land on a multiple of 36.
The practical consequence is that a GSTIN with one wrong or transposed character is structurally perfect and arithmetically impossible. It passes any regex you write and fails the checksum. That is why eyeballing the format is not enough, and why a number that looks completely ordinary can still be fabricated ā a distinction that matters when you are recording a supplier on an invoice you intend to claim input tax credit against.
Frequently Asked Questions
Does a valid check digit mean the GSTIN is registered?
No. It proves the number is well-formed and internally consistent, which rules out typos and most fabrications. Whether that registration exists and is currently active can only be confirmed on the official GST portal.
Is my GST number sent to a server?
No. The entire calculation runs in your browser in JavaScript. Nothing is uploaded, logged or stored, so it is safe to check client and supplier numbers here.
What does the 14th character āZā mean?
It is a fixed placeholder in the current scheme, reserved for future use. Almost every GSTIN has Z in that position, and this tool expects it.
Why does a GSTIN I copied from an invoice fail?
Usually a transposition ā two adjacent characters swapped ā or a letter O read as a zero, or the digit 1 read as the letter I. The tool shows the check character it expected, which makes the mistake easier to find.
Can I get the PAN from a GSTIN?
Yes. Characters 3 to 12 of a GSTIN are the holder's PAN, and this tool extracts it for you along with the holder type encoded in it.
What do the first two digits mean?
They are the state code of the registration ā 27 for Maharashtra, 29 for Karnataka, 07 for Delhi, and so on. A business registered in several states has a separate GSTIN per state, all sharing the same PAN.
Can AI agents check GST numbers too?
Yes. The same validation is available as validate_gstin on our MCP server, so Claude, Cursor and other MCP-capable agents can verify a number instead of guessing at it ā which language models do badly, since the check digit has to be computed rather than recalled.