TAN

Validates a Tax Deduction and Collection Account Number (TAN): 10 characters — 4 letters, 5 digits, 1 letter. TAN is issued by the Income Tax Department to anyone who deducts or collects tax at source (TDS/TCS).

Rules

Rule	Detail
Format	^[A-Z]{4}[0-9]{5}[A-Z]$
Length	Exactly 10 characters
1st–3rd characters	Jurisdiction code (e.g. MUM = Mumbai, DEL = Delhi)
4th character	First initial of the deductor’s name
5th–9th characters	System-generated sequence number
10th character	System-generated check letter
Checksum	None — format only, no public checksum. The last letter is a check character, but its algorithm is not published, so indycheck cannot verify it

Usage

import { validateTan } from 'indycheck';

validateTan('MUMB12345C');
// { ok: true, code: 'VALID', normalized: 'MUMB12345C',
//   parsed: { tan: 'MUMB12345C' } }

from indycheck import validate_tan

validate_tan("MUMB12345C").ok  # True

use indycheck::validate_tan;

let r = validate_tan("MUMB12345C");
assert!(r.ok);

Examples

Input	Result	Code
MUMB12345C	Valid	VALID
DELH12345A	Valid	VALID
mumb12345c	Valid (normalised)	VALID
MUMB1234C	Invalid — 9 characters	INVALID_LENGTH
MUM12345C	Invalid — 9 characters	INVALID_LENGTH
MUMB123455	Invalid — last char must be a letter	INVALID_FORMAT
MUMB12A45C	Invalid — letter inside the digits	INVALID_FORMAT
(empty)	Invalid	EMPTY

Error codes

Code	Means
EMPTY	Nothing was passed in
INVALID_LENGTH	Not exactly 10 characters
INVALID_FORMAT	Doesn’t match 4 letters + 5 digits + 1 letter

Parsed output

On success, parsed contains:

{
  "tan": "MUMB12345C"
}

Honest limits — format only

TAN has no public checksum, so indycheck can only check the shape. A well-formed TAN may still be unissued or belong to someone else. Real verification needs the Income Tax Department’s TAN search. Do not confuse TAN with PAN — both are 10 characters, but PAN is 5 letters + 4 digits + 1 letter, while TAN is 4 letters + 5 digits + 1 letter.