dsh-checkdigit

Check-digit mathematics toolbox for DeepSeek Harness (dsh): generate, validate, repair and detect check digits for 15 schemes — Luhn, Verhoeff, Damm, ISBN-10, ISBN-13, EAN-8, EAN-13, UPC-A, GTIN-14, ISSN, ISIN, CUSIP, IBAN, CAS Registry Number and ABA routing number — plus an ISBN-10 ⇄ ISBN-13 converter and a single-edit repair search ("what was this number most likely meant to be?").

校验位数学工具箱：生成 / 验证 / 修复 / 识别 15 种校验位（Luhn、Verhoeff、Damm、ISBN、EAN、UPC、GTIN-14、ISSN、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、以及「单字符修复」搜索工具；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:

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 → ISSN (X-terminated) → 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, dashes and dots in the input are ignored (the spaced card form 4111 1111 1111 1111, the hyphenated 978-0-306-40615-7 and the printed 0378-5955 all validate). When a value is invalid, the result carries the expected check digit so callers can fix it programmatically.

checkdigit_repair

When a value fails, enumerate the single-character edits that make it valid — a corrected check character, a swapped adjacent pair, or one mistyped payload character. Every repair is confirmed by the scheme's own validator and ordered most-likely-first.

checkdigit_repair(value="79927398714")
→ scheme: "luhn", total: 12, checkDigit: "4", expected: "3"
  repairs[0]: { type: "check-digit", position: 11, from: "4", to: "3", value: "79927398713" }

checkdigit_repair(value="GB82WEST12345698765431")
→ scheme: "iban", total: 7
  repairs[0]: { type: "check-digit", position: 3, to: "12", value: "GB12WEST12345698765431" }   # keep the account
  repairs[6]: { type: "substitute", position: 22, from: "1", to: "2", value: "GB82WEST12345698765432" }  # keep the check digits

Both IBAN answers are legitimate — the caller can see whether the account digits or the check digits were more likely mistyped. total always reports the full count; the returned list is capped at 20 (truncated: true).

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 15.

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

Development

pnpm install
pnpm build
pnpm test   # 91 tests
pnpm lint
python3 test/oracle/anchors.py   # independent anchors for every numeric assertion

Test expectations are not hand-computed: test/oracle/anchors.py re-implements each scheme from its published specification in Python and prints every anchor the suites assert, including the repair counts and positions. Run it (or pnpm test on a fresh checkout) to regenerate them.

License

MIT