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About this tool
Validate Indian GSTIN format, decode state code, extract PAN, verify checksum, mask output, and check bulk GSTIN lists locally.
The GSTIN Format Validator checks a 15-character GSTIN against its published structure — 2-digit state code, 10-character PAN, entity code, the fixed letter Z, and a mod-36 check character — and tells you which part failed. It decodes the state, extracts the embedded PAN, recomputes the checksum with the alternating 2/1 weighting used by the GST system, and produces a masked version safe to share. Single GSTINs and pasted bulk lists both run locally, and the list can be exported as CSV.
Open GSTIN Format Validator on AltFTool — it loads instantly in your browser.
Type a 15-character GSTIN into the "GSTIN number" field (formatted like 29 ABCDE1234F 1Z 5), or switch to Bulk List and paste GSTINs one per line.
The breakdown updates as you type: decoded state, embedded PAN, entity code, checksum status and the expected check character when the 15th character is wrong, with a masked version safe to share.
Press "Copy Masked" to copy share-safe values, or CSV to download gstin-format-validation.csv with the full per-GSTIN breakdown and issues.
Reports the specific failure — bad state code, PAN pattern, entity code, missing Z or checksum mismatch — not just pass or fail.
When the 15th character is wrong it shows the character the mod-36 algorithm actually expects.
Paste a whole list separated by newlines, commas or semicolons; copy masked values or download the full breakdown as CSV.
A GSTIN is 15 characters: positions 1–2 are the state code, 3–12 are the holder's PAN, 13 is the entity number for that PAN within the state, 14 is the letter Z, and 15 is a checksum character. So 29ABCDE1234F1ZW is a Karnataka (29) registration on PAN ABCDE1234F.
It is a mod-36 checksum over the first 14 characters. Each character is mapped to its value in the set 0–9 then A–Z, multiplied by an alternating factor of 2 and 1 working right to left, and the quotient and remainder of that product divided by 36 are added together; the check character is the symbol at (36 − sum mod 36) mod 36.
No. Structure and checksum validation only prove the number is well formed — a cancelled, suspended or never-issued GSTIN can still pass all 15-character checks. Confirm live registration status on the official GST portal before relying on it for input tax credit.
They are the GST state code, running from 01 (Jammu & Kashmir) through 38 (Ladakh), with 97 reserved for Other Territory. Common ones are 07 Delhi, 24 Gujarat, 27 Maharashtra, 29 Karnataka, 33 Tamil Nadu and 36 Telangana; anything outside the recognised list is flagged as an invalid state code.
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