The validation gate
Most tools show what the model guessed. We check the math first. Checksums, HSN, does it add up. The entry has to earn its place.
Nothing wrong reaches Tally. Try it.
Most tools show a guess. We check it. Checksums. Directory. Does the math on the page add up.
Below is a real invoice from the test corpus. Pick a scenario and run the gates.
The four gates
Each gate is cheap to run and expensive to fool. Together they make wrong entries provably unlikely instead of probably rare.
GSTIN mod-36 checksum
A GSTIN’s fifteenth character is a check digit computed over the first fourteen. Transposed digits, O-vs-0 swaps and scanner misreads break it predictably, which is exactly what you want from a gate: cheap to verify, hard to pass by luck.
HSN directory
Every line’s HSN code is checked for format and membership in the directory, so line items name goods that actually exist under the code the scan claims.
Arithmetic closure
Line items must sum to taxable value; taxable value times rate must equal the taxes; taxes plus taxable must equal the grand total. If the invoice’s own math closes, the numbers are almost certainly read right.
Regime consistency
Place of supply decides CGST plus SGST versus IGST. Intra-state invoices claiming IGST, or the reverse, stop at the gate instead of your books.
When something fails, your operator sees this
Only failures reach a human. The scan sits beside the extracted fields, the failing check is highlighted, and a fix is usually a single keystroke. Everything confirmed is logged against the invoice.
This preview is live: the scanner misread one character of the seller's GSTIN. Correct it and watch the checksum gate flip to green.
Verified
fix the GSTIN above; the checksum gate re-runs as you type
Try it: change G to 6 in the GSTIN field.
Every field carries its evidence
Each exported entry carries the scan crop it came from, the validator results, and who confirmed what, if anyone did. When a GST notice arrives, the answer is a one-page trail per invoice, not an afternoon in filing cabinets.