dsh-checkdigit

Check-digit mathematics toolbox for DeepSeek Harness (dsh): generate, validate and detect check digits for 13 schemes — Luhn, Verhoeff, Damm, ISBN-10, ISBN-13, EAN-8, EAN-13, UPC-A, ISIN, CUSIP, IBAN, CAS Registry Number and ABA routing number — plus an ISBN-10 ⇄ ISBN-13 converter.

校验位数学工具箱：生成 / 验证 / 识别 13 种校验位（Luhn、Verhoeff、Damm、ISBN、EAN、UPC、ISIN、CUSIP、IBAN、CAS 化学文摘号、ABA 美国银行路由号），另带 ISBN-10 与 ISBN-13 互转工具；零运行时依赖、纯本地算术。

Why

Language models routinely botch check-digit arithmetic: wrong card-number checksums, ISBNs that fail validation, IBANs with impossible check digits. Every algorithm here is implemented from its published specification with pure integer arithmetic — deterministic, offline, zero runtime dependencies — and cross-checked against published worked examples (Apple's US0378331005, the classic GB82 WEST 1234 5698 7654 32, the Luhn textbook example 79927398713, water's CAS number 7732-18-5, and more).

Install

dsh plugin --profile web add github:TYEclipse/dsh-checkdigit

Then add dsh-checkdigit to dsh.profile.bundles in your profile's package.json if it is not auto-activated, and restart dsh.

Tools

checkdigit_generate

Compute the check digit for a payload and return the complete identifier.

checkdigit_generate(scheme="luhn", payload="7992739871")
→ checkDigit: "3", complete: "79927398713"

Supported scheme values and their payloads:

scheme	payload	check digit	example complete
luhn	digits (any length ≥ 1)	last digit	79927398713
verhoeff	digits (any length ≥ 1)	last digit	2363
damm	digits (any length ≥ 1)	last digit	5724
isbn10	9 digits	10th char (0-9 or X)	0306406152
isbn13	12 digits	13th digit	9780306406157
ean8	7 digits	8th digit	96385074
ean13	12 digits	13th digit	4006381333931
upca	11 digits	12th digit	036000291452
isin	2 letters + 9 alphanumerics	12th char (digit)	US0378331005
cusip	8 chars from [A-Z0-9*@#]	9th char (digit)	037833100
iban	2-letter country + BBAN	chars 3–4 (two digits)	GB82WEST12345698765432
cas	2–9 digits (hyphens ignored)	last digit	7732-18-5
aba	8 digits	9th digit	021000021

Use it to build test card numbers, ISBNs, barcodes, securities identifiers, routing numbers or account numbers whose check digits actually verify.

checkdigit_validate

Verify the check digit of a full identifier. The scheme is auto-detected when omitted (CAS hyphenated → ISIN → 9-digit ABA → CUSIP → IBAN → EAN-13 → UPC-A → EAN-8 → ISBN-10 → Luhn); pass scheme to force one.

checkdigit_validate(value="GB82WEST12345698765432")
→ valid: true, scheme: "iban", iban.country: "GB", iban.formatted: "GB82 WEST 1234 5698 7654 32"

checkdigit_validate(value="7732-18-5")
→ valid: true, scheme: "cas", checkDigit: "5"

checkdigit_validate(value="021000021")
→ valid: true, scheme: "aba", checkDigit: "1"

checkdigit_validate(value="79927398714")
→ valid: false, scheme: "luhn", checkDigit: "4", expected: "3",
  detail: "Luhn: check digit should be 3, but the value ends in 4"

Spaces and dashes in the input are ignored. When a value is invalid, the result carries the expected check digit so callers can fix it programmatically.

checkdigit_info

Describe the supported schemes: identifier lengths, payload formats, check-digit positions and worked examples. Call with a scheme for one scheme, or without arguments for all 13.

isbn_convert

Convert between ISBN-10 and ISBN-13 in both directions. The source check digit is verified first; the 978 Bookland prefix is prepended (10→13) or dropped (13→10) and the target check digit recomputed. Hyphen grouping from the input is preserved in formatted.

isbn_convert(isbn="0-306-40615-2")
→ valid: true, direction: "to13", converted: "9780306406157", formatted: "978-0-306-40615-7"

isbn_convert(isbn="978-0-306-40615-7")
→ valid: true, direction: "to10", converted: "0306406152", formatted: "0-306-40615-2"

isbn_convert(isbn="9791090636071")
→ valid: false, error: "ISBN-13 with the 979 prefix has no ISBN-10 equivalent; only the 978 Bookland prefix maps back to ISBN-10"

ISBN-10 check digits may be X (value 10): 0-8044-2957-X → 978-0-8044-2957-3.

Supported schemes

Scheme	Standard	Detail
Luhn	ISO/IEC 7812	Credit/debit cards, IMEI, loyalty cards
Verhoeff	—	Dihedral-group checksum; catches all single errors and adjacent transpositions
Damm	—	Quasigroup operation; full-value tally must be zero
ISBN-10	ISO 2108	Mod-11; check digit may be X (= 10)
ISBN-13	ISO 2108	EAN-13 arithmetic (Bookland)
EAN-8 / EAN-13	GS1 GTIN-8 / GTIN-13	Retail barcodes
UPC-A	GS1 GTIN-12	North American retail barcodes
ISIN	ISO 6166	Securities; letters expand A=10…Z=35, then Luhn
CUSIP	ANSI X9.6	North American securities; * @ # allowed; even positions doubled
IBAN	ISO 13616	Mod-97 over letter-expanded rearranged string; BBAN length table for 75+ countries
CAS Registry Number	CAS	Chemical substances; digit × position-from-right sum mod 10
ABA routing number	US Federal Reserve	Bank routing transit numbers; 3-7-1 weighted sum mod 10

Development

pnpm install
pnpm build
pnpm test   # 67 tests, anchors cross-checked against published worked examples
pnpm lint

License

MIT