Validate or compute check digits for Luhn, GTIN/EAN/UPC, ISBN, ISSN, IMEI, ISIN, LEI, VIN, NPI, ABA and ISO 7064 — one cited algorithm per scheme.
Authoritative reference data or standards computation
One record per scheme with its algorithm, alphabet, length rules, applicability scope, error-detection limits and specification reference.
| Parameter | Type | Default & allowed | Description |
|---|---|---|---|
search | string | allowed: 1 – 40 example: isbn | Case-insensitive filter: any substring of the scheme id or name, or the start of any word in the algorithm description (so 'luhn' also finds imei, npi and isin). No match returns an empty list plus a warning — never a substitute scheme. |
search string Case-insensitive filter: any substring of the scheme id or name, or the start of any word in the algorithm description (so 'luhn' also finds imei, npi and isin). No match returns an empty list plus a warning — never a substitute scheme.
| Parameter | Type | Default & allowed | Description |
|---|---|---|---|
count | int | default: 20 allowed: 1 – 100 example: 3 | Limit the number of returned records (1–100). Defaults to 20. |
fields | list | example: scheme,name | Return only these fields (comma-separated). Mutually exclusive with 'exclude'. |
exclude | list | example: meaning | Return all fields except these (comma-separated). |
format | enum | default: json allowed: json | ndjson | csv example: csv | Response format: json envelope, ndjson (one record per line) or csv. |
pretty | boolean | default: false example: true | Pretty-print the JSON response. |
unwrap | boolean | default: false example: true | Drop the envelope: return the raw array/object without data/meta wrapper. |
count int Limit the number of returned records (1–100). Defaults to 20.
fields list Return only these fields (comma-separated). Mutually exclusive with 'exclude'.
exclude list Return all fields except these (comma-separated).
format enum Response format: json envelope, ndjson (one record per line) or csv.
pretty boolean Pretty-print the JSON response.
unwrap boolean Drop the envelope: return the raw array/object without data/meta wrapper.
| Field | Type | Description | Example |
|---|---|---|---|
scheme | string | Scheme id used by the scheme parameter. | gtin13 |
name | string | Human name of the identifier scheme. | GTIN-13 (EAN-13) |
algorithm | string | The check-character algorithm in one sentence. | GS1 modulo-10: weights 3 and 1 alternating from the right, subtracted from the next multiple of ten |
alphabet | string | Characters allowed in the payload. | 0-9 |
lengths | integer[] | Accepted total lengths including the check characters. Empty for variable-length schemes. | [13] |
minLength | integer | Smallest accepted total length — the only length rule for variable-length schemes. | 13 |
checkCharacters | integer | Number of check characters: 1 for most schemes, 2 for MOD 97-10 and LEI. | 1 |
checkAlphabet | string | Characters the check position may hold. | 0-9 |
checkPosition | string | Where the check characters sit in the identifier. | last character |
scope | string | Where the scheme (and its check character) actually applies — regional limits are stated here. | Global GS1 key, printed as an EAN-13 symbol. |
strictRules nullable | string | What strict=true adds on /validate, or null when the alphabet, length and check character are the whole format. | null |
detectsAllSingleCharacterErrors | boolean | Whether every single-character substitution changes the check character. | true |
undetectedSubstitutions nullable | string | Which single-character changes slip through, or null when none do. | null |
detectsAllAdjacentTranspositions | boolean | Whether swapping any two adjacent characters changes the check character. | false |
undetectedTranspositions nullable | string | Which adjacent swaps slip through, or null when none do. | Swapping two adjacent digits whose values differ by five is undetected (05↔50, 16↔61, 27↔72, 38↔83, 49↔94). Every other adjacent transposition changes the check digit. |
specification | string | The published specification this implementation follows. | GS1 General Specifications — check-digit calculation |
specificationUrl nullable | string | Public page for the specification, or null when only a paywalled standard exists. | https://www.gs1.org/standards/barcodes/ean-upc |
meaning | string | What a valid check character does and does not prove for this scheme. | A correct check digit means the digits are internally consistent. It does not mean the GTIN has been allocated to a company or assigned to a product — this endpoint queries no GS1 registry and holds no product catalogue. |
scheme string Scheme id used by the scheme parameter.
example: gtin13
name string Human name of the identifier scheme.
example: GTIN-13 (EAN-13)
algorithm string The check-character algorithm in one sentence.
example: GS1 modulo-10: weights 3 and 1 alternating from the right, subtracted from the next multiple of ten
alphabet string Characters allowed in the payload.
example: 0-9
lengths integer[] Accepted total lengths including the check characters. Empty for variable-length schemes.
example: [13]
minLength integer Smallest accepted total length — the only length rule for variable-length schemes.
example: 13
checkCharacters integer Number of check characters: 1 for most schemes, 2 for MOD 97-10 and LEI.
example: 1
checkAlphabet string Characters the check position may hold.
example: 0-9
checkPosition string Where the check characters sit in the identifier.
example: last character
scope string Where the scheme (and its check character) actually applies — regional limits are stated here.
example: Global GS1 key, printed as an EAN-13 symbol.
strictRules string nullable What strict=true adds on /validate, or null when the alphabet, length and check character are the whole format.
example: null
detectsAllSingleCharacterErrors boolean Whether every single-character substitution changes the check character.
example: true
undetectedSubstitutions string nullable Which single-character changes slip through, or null when none do.
example: null
detectsAllAdjacentTranspositions boolean Whether swapping any two adjacent characters changes the check character.
example: false
undetectedTranspositions string nullable Which adjacent swaps slip through, or null when none do.
example: Swapping two adjacent digits whose values differ by five is undetected (05↔50, 16↔61, 27↔72, 38↔83, 49↔94). Every other adjacent transposition changes the check digit.
specification string The published specification this implementation follows.
example: GS1 General Specifications — check-digit calculation
specificationUrl string nullable Public page for the specification, or null when only a paywalled standard exists.
example: https://www.gs1.org/standards/barcodes/ean-upc
meaning string What a valid check character does and does not prove for this scheme.
example: A correct check digit means the digits are internally consistent. It does not mean the GTIN has been allocated to a company or assigned to a product — this endpoint queries no GS1 registry and holds no product catalogue.
/api/check-digits {
"data": [
{
"scheme": "luhn",
"name": "Luhn (generic mod-10)",
"algorithm": "Luhn modulo-10: double every second digit from the right, add the digits of any result above nine, subtract the total from the next multiple of ten",
"alphabet": "0-9",
"lengths": [],
"minLength": 2,
"checkCharacters": 1,
"checkAlphabet": "0-9",
"checkPosition": "last character",
"scope": "Global. The generic algorithm behind payment card numbers, IMEIs, NPIs and the final step of an ISIN.",
"strictRules": null,
"detectsAllSingleCharacterErrors": true,
"undetectedSubstitutions": null,
"detectsAllAdjacentTranspositions": false,
"undetectedTranspositions": "Swapping an adjacent 0 and 9 is undetected, because both digits map to themselves when doubled. Every other adjacent transposition changes the check digit.",
"specification": "ISO/IEC 7812-1, Annex B",
"specificationUrl": "https://www.iso.org/standard/70484.html",
"meaning": "A correct Luhn digit means the digit string is internally consistent. On its own it says nothing about what the number identifies, who issued it or whether it was ever allocated."
},
{
"scheme": "gtin8",
"name": "GTIN-8 (EAN-8)",
"algorithm": "GS1 modulo-10: weights 3 and 1 alternating from the right, subtracted from the next multiple of ten",
"alphabet": "0-9",
"lengths": [
8
],
"minLength": 8,
"checkCharacters": 1,
"checkAlphabet": "0-9",
"checkPosition": "last character",
"scope": "Global GS1 key for very small packaging.",
"strictRules": null,
"detectsAllSingleCharacterErrors": true,
"undetectedSubstitutions": null,
"detectsAllAdjacentTranspositions": false,
"undetectedTranspositions": "Swapping two adjacent digits whose values differ by five is undetected (05↔50, 16↔61, 27↔72, 38↔83, 49↔94). Every other adjacent transposition changes the check digit.",
…
"generatedAt": "2026-07-29T08:13:22.000Z"
}
} /api/check-digits?search=luhn {
"data": [
{
"scheme": "luhn",
"name": "Luhn (generic mod-10)",
"algorithm": "Luhn modulo-10: double every second digit from the right, add the digits of any result above nine, subtract the total from the next multiple of ten",
"alphabet": "0-9",
"lengths": [],
"minLength": 2,
"checkCharacters": 1,
"checkAlphabet": "0-9",
"checkPosition": "last character",
"scope": "Global. The generic algorithm behind payment card numbers, IMEIs, NPIs and the final step of an ISIN.",
"strictRules": null,
"detectsAllSingleCharacterErrors": true,
"undetectedSubstitutions": null,
"detectsAllAdjacentTranspositions": false,
"undetectedTranspositions": "Swapping an adjacent 0 and 9 is undetected, because both digits map to themselves when doubled. Every other adjacent transposition changes the check digit.",
"specification": "ISO/IEC 7812-1, Annex B",
"specificationUrl": "https://www.iso.org/standard/70484.html",
"meaning": "A correct Luhn digit means the digit string is internally consistent. On its own it says nothing about what the number identifies, who issued it or whether it was ever allocated."
},
{
"scheme": "imei",
"name": "IMEI",
"algorithm": "Luhn modulo-10 over the fourteen TAC and serial digits",
"alphabet": "0-9",
"lengths": [
15
],
"minLength": 15,
"checkCharacters": 1,
"checkAlphabet": "0-9",
"checkPosition": "last character",
"scope": "Global, for GSM/UMTS/LTE/NR mobile equipment.",
"strictRules": null,
"detectsAllSingleCharacterErrors": true,
"undetectedSubstitutions": null,
"detectsAllAdjacentTranspositions": false,
"undetectedTranspositions": "Swapping an adjacent 0 and 9 is undetected, because both digits map to themselves when doubled. Every other adjacent transposition changes the check digit.",
…
"generatedAt": "2026-07-29T08:13:22.000Z"
}
} /api/check-digits?search=gtin&format=csv scheme,name,algorithm,alphabet,lengths,minLength,checkCharacters,checkAlphabet,checkPosition,scope,strictRules,detectsAllSingleCharacterErrors,undetectedSubstitutions,detectsAllAdjacentTranspositions,undetectedTranspositions,specification,specificationUrl,meaning
gtin8,GTIN-8 (EAN-8),"GS1 modulo-10: weights 3 and 1 alternating from the right, subtracted from the next multiple of ten",0-9,[8],8,1,0-9,last character,Global GS1 key for very small packaging.,,true,,false,"Swapping two adjacent digits whose values differ by five is undetected (05↔50, 16↔61, 27↔72, 38↔83, 49↔94). Every other adjacent transposition changes the check digit.",GS1 General Specifications — check-digit calculation,https://www.gs1.org/standards/barcodes/ean-upc,A correct check digit means the digits are internally consistent. It does not mean the GTIN has been allocated to a company or assigned to a product — this endpoint queries no GS1 registry and holds no product catalogue.
gtin12,GTIN-12 (UPC-A),"GS1 modulo-10: weights 3 and 1 alternating from the right, subtracted from the next multiple of ten",0-9,[12],12,1,0-9,last character,"Global GS1 key, printed as a UPC-A symbol and used mainly in North America.",,true,,false,"Swapping two adjacent digits whose values differ by five is undetected (05↔50, 16↔61, 27↔72, 38↔83, 49↔94). Every other adjacent transposition changes the check digit.",GS1 General Specifications — check-digit calculation,https://www.gs1.org/standards/barcodes/ean-upc,A correct check digit means the digits are internally consistent. It does not mean the GTIN has been allocated to a company or assigned to a product — this endpoint queries no GS1 registry and holds no product catalogue.
gtin13,GTIN-13 (EAN-13),"GS1 modulo-10: weights 3 and 1 alternating from the right, subtracted from the next multiple of ten",0-9,[13],13,1,0-9,last character,"Global GS1 key, printed as an EAN-13 symbol.",,true,,false,"Swapping two adjacent digits whose values differ by five is undetected (05↔50, 16↔61, 27↔72, 38↔83, 49↔94). Every other adjacent transposition changes the check digit.",GS1 General Specifications — check-digit calculation,https://www.gs1.org/standards/barcodes/ean-upc,A correct check digit means the digits are internally consistent. It does not mean the GTIN has been allocated to a company or assigned to a product — this endpoint queries no GS1 registry and holds no product catalogue.
gtin14,GTIN-14 (ITF-14 case code),"GS1 modulo-10: weights 3 and 1 alternating from the right, subtracted from the next multiple of ten",0-9,[14],14,1,0-9,last character,Global GS1 key for higher packaging levels; the first digit is the packaging indicator.,,true,,false,"Swapping two adjacent digits whose values differ by five is undetected (05↔50, 16↔61, 27↔72, 38↔83, 49↔94). Every other adjacent transposition changes the check digit.",GS1 General Specifications — check-digit calculation,https://www.gs1.org/standards/barcodes/ean-upc,A correct check digit means the digits are internally consistent. It does not mean the GTIN has been allocated to a company or assigned to a product — this endpoint queries no GS1 registry and holds no product catalogue.
Returns a structured verdict for any input: malformed values produce valid=false with ordered reason codes, never an error page.
| Parameter | Type | Default & allowed | Description |
|---|---|---|---|
scheme
required
| enum | allowed: luhn | gtin8 | gtin12 | gtin13 | gtin14 | upca | isbn10 | isbn13 | issn | ismn | imei | isin | lei | vin | npi | aba | iso7064-mod11-2 | iso7064-mod11-10 | iso7064-mod97-10 example: isbn13 | Identifier scheme to apply. 'upca' is an alias for 'gtin12'. 'npi' and 'aba' are United States schemes, and the 'vin' check character is only enforced where the world manufacturer identifier's ISO 3780 region block is North American (1-5) or Chinese (L). |
value
required
| string | allowed: 1 – 64 example: 978-0-306-40615-7 | The identifier to check, with or without spaces and hyphens. Whitespace is preserved when normalize=false so it shows up as an invalid character. |
normalize | boolean | default: true example: true | Remove ASCII spaces and hyphens before checking. ASCII letters are uppercased either way, because every scheme's alphabet is uppercase-only. |
strict | boolean | default: false example: true | Also enforce the scheme's structural rules (prefixes, VIN model-year code, Federal Reserve routing symbol). Schemes with no further rules answer with a warning. |
scheme enum required Identifier scheme to apply. 'upca' is an alias for 'gtin12'. 'npi' and 'aba' are United States schemes, and the 'vin' check character is only enforced where the world manufacturer identifier's ISO 3780 region block is North American (1-5) or Chinese (L).
value string required The identifier to check, with or without spaces and hyphens. Whitespace is preserved when normalize=false so it shows up as an invalid character.
normalize boolean Remove ASCII spaces and hyphens before checking. ASCII letters are uppercased either way, because every scheme's alphabet is uppercase-only.
strict boolean Also enforce the scheme's structural rules (prefixes, VIN model-year code, Federal Reserve routing symbol). Schemes with no further rules answer with a warning.
| Parameter | Type | Default & allowed | Description |
|---|---|---|---|
fields | list | example: scheme,canonicalScheme | Return only these fields (comma-separated). Mutually exclusive with 'exclude'. |
exclude | list | example: notes | Return all fields except these (comma-separated). |
pretty | boolean | default: false example: true | Pretty-print the JSON response. |
unwrap | boolean | default: false example: true | Drop the envelope: return the raw array/object without data/meta wrapper. |
fields list Return only these fields (comma-separated). Mutually exclusive with 'exclude'.
exclude list Return all fields except these (comma-separated).
pretty boolean Pretty-print the JSON response.
unwrap boolean Drop the envelope: return the raw array/object without data/meta wrapper.
| Field | Type | Description | Example |
|---|---|---|---|
scheme | string | Scheme id exactly as requested. | isbn13 |
canonicalScheme | string | Scheme actually applied — 'upca' resolves to 'gtin12'. | isbn13 |
input | string | The value exactly as supplied. | 978-0-306-40615-7 |
normalized | string | Uppercased value, with ASCII spaces and hyphens removed when normalize is true. | 9780306406157 |
valid | boolean | True only for this endpoint's checks: alphabet, length, check character (where applicable) and any strict rules. It never means the identifier was issued, assigned or registered. | true |
reasons | string[] | Stable ordered failure codes — EMPTY_AFTER_NORMALIZATION, INVALID_CHARACTERS, WRONG_LENGTH, CHECK_CHARACTER_MISMATCH, STRICT_INVALID_PREFIX, STRICT_INVALID_MODEL_YEAR_CODE, STRICT_INVALID_ROUTING_SYMBOL. Empty exactly when valid is true. | [] |
payload nullable | string | The value without its check characters, or null when the value was too malformed to split. | 978030640615 |
checkCharacter nullable | string | The check character(s) found in the input, or null when the value could not be split. | 7 |
expectedCheckCharacter nullable | string | What the scheme's algorithm computes for that payload, or null when it could not be computed. | 7 |
checkCharacterValid | boolean | Whether the supplied check character equals the computed one. Reported even when checkDigitApplicable is false, so a European VIN's position-9 result is still visible. | true |
checkDigitApplicable | boolean | Whether this endpoint holds the check character against the value. Always true except for a complete VIN whose world manufacturer identifier falls outside the ISO 3780 North American (1-5) and Chinese (L) region blocks, where a mismatch never makes the VIN invalid. That is inferred from the WMI alone, so false means 'not determinable from the VIN alone', not 'not required' — 49 CFR 565 requires a check digit on any vehicle built for sale in the US whatever its WMI. Read checkCharacterValid for the strict answer. | true |
actualLength | integer | Length of the normalized value. | 13 |
expectedLengths | integer[] | Accepted total lengths, or an empty array for a variable-length scheme. | [13] |
minLength | integer | Smallest accepted total length. | 13 |
invalidCharacters | object[] | Every character outside the scheme's alphabet, in input order, as { index, character } with a zero-based index into the normalized value. When the length is wrong the check position cannot be located, so every character is tested against the scheme's full alphabet rather than the narrower check-position one. Empty when the alphabet check passed. | [{"index":4,"character":"#"}] |
algorithm | string | The algorithm applied, in one sentence. | GS1 modulo-10 over the thirteen-digit Bookland EAN (weights 3 and 1 alternating from the right) |
scope | string | Where this scheme and its check character actually apply. | Global. |
notes | string[] | Situational explanations — VIN regional applicability, the upca alias, a 16-digit IMEISV, a failed strict rule, and the GS1 prefix caveat on every GTIN form. Empty when nothing needs saying. | [] |
scheme string Scheme id exactly as requested.
example: isbn13
canonicalScheme string Scheme actually applied — 'upca' resolves to 'gtin12'.
example: isbn13
input string The value exactly as supplied.
example: 978-0-306-40615-7
normalized string Uppercased value, with ASCII spaces and hyphens removed when normalize is true.
example: 9780306406157
valid boolean True only for this endpoint's checks: alphabet, length, check character (where applicable) and any strict rules. It never means the identifier was issued, assigned or registered.
example: true
reasons string[] Stable ordered failure codes — EMPTY_AFTER_NORMALIZATION, INVALID_CHARACTERS, WRONG_LENGTH, CHECK_CHARACTER_MISMATCH, STRICT_INVALID_PREFIX, STRICT_INVALID_MODEL_YEAR_CODE, STRICT_INVALID_ROUTING_SYMBOL. Empty exactly when valid is true.
example: []
payload string nullable The value without its check characters, or null when the value was too malformed to split.
example: 978030640615
checkCharacter string nullable The check character(s) found in the input, or null when the value could not be split.
example: 7
expectedCheckCharacter string nullable What the scheme's algorithm computes for that payload, or null when it could not be computed.
example: 7
checkCharacterValid boolean Whether the supplied check character equals the computed one. Reported even when checkDigitApplicable is false, so a European VIN's position-9 result is still visible.
example: true
checkDigitApplicable boolean Whether this endpoint holds the check character against the value. Always true except for a complete VIN whose world manufacturer identifier falls outside the ISO 3780 North American (1-5) and Chinese (L) region blocks, where a mismatch never makes the VIN invalid. That is inferred from the WMI alone, so false means 'not determinable from the VIN alone', not 'not required' — 49 CFR 565 requires a check digit on any vehicle built for sale in the US whatever its WMI. Read checkCharacterValid for the strict answer.
example: true
actualLength integer Length of the normalized value.
example: 13
expectedLengths integer[] Accepted total lengths, or an empty array for a variable-length scheme.
example: [13]
minLength integer Smallest accepted total length.
example: 13
invalidCharacters object[] Every character outside the scheme's alphabet, in input order, as { index, character } with a zero-based index into the normalized value. When the length is wrong the check position cannot be located, so every character is tested against the scheme's full alphabet rather than the narrower check-position one. Empty when the alphabet check passed.
example: [{"index":4,"character":"#"}]
algorithm string The algorithm applied, in one sentence.
example: GS1 modulo-10 over the thirteen-digit Bookland EAN (weights 3 and 1 alternating from the right)
scope string Where this scheme and its check character actually apply.
example: Global.
notes string[] Situational explanations — VIN regional applicability, the upca alias, a 16-digit IMEISV, a failed strict rule, and the GS1 prefix caveat on every GTIN form. Empty when nothing needs saying.
example: []
/api/check-digits/validate?scheme=isbn13&value=978-0-306-40615-7 {
"data": {
"scheme": "isbn13",
"canonicalScheme": "isbn13",
"input": "978-0-306-40615-7",
"normalized": "9780306406157",
"valid": true,
"reasons": [],
"payload": "978030640615",
"checkCharacter": "7",
"expectedCheckCharacter": "7",
"checkCharacterValid": true,
"checkDigitApplicable": true,
"actualLength": 13,
"expectedLengths": [
13
],
"minLength": 13,
"invalidCharacters": [],
"algorithm": "GS1 modulo-10 over the thirteen-digit Bookland EAN (weights 3 and 1 alternating from the right)",
"scope": "Global.",
"notes": []
},
"meta": {
"endpoint": "check-digits",
"route": "/validate",
"params": {
"scheme": "isbn13",
"value": "978-0-306-40615-7",
"normalize": true,
"strict": false
},
"generatedAt": "2026-07-29T08:13:22.000Z"
}
} /api/check-digits/validate?scheme=imei&value=490154203237518 {
"data": {
"scheme": "imei",
"canonicalScheme": "imei",
"input": "490154203237518",
"normalized": "490154203237518",
"valid": true,
"reasons": [],
"payload": "49015420323751",
"checkCharacter": "8",
"expectedCheckCharacter": "8",
"checkCharacterValid": true,
"checkDigitApplicable": true,
"actualLength": 15,
"expectedLengths": [
15
],
"minLength": 15,
"invalidCharacters": [],
"algorithm": "Luhn modulo-10 over the fourteen TAC and serial digits",
"scope": "Global, for GSM/UMTS/LTE/NR mobile equipment.",
"notes": []
},
"meta": {
"endpoint": "check-digits",
"route": "/validate",
"params": {
"scheme": "imei",
"value": "490154203237518",
"normalize": true,
"strict": false
},
"generatedAt": "2026-07-29T08:13:22.000Z"
}
} /api/check-digits/validate?scheme=vin&value=WVWZZZ1JZXW000010 {
"data": {
"scheme": "vin",
"canonicalScheme": "vin",
"input": "WVWZZZ1JZXW000010",
"normalized": "WVWZZZ1JZXW000010",
"valid": true,
"reasons": [],
"payload": "WVWZZZ1JXW000010",
"checkCharacter": "Z",
"expectedCheckCharacter": "1",
"checkCharacterValid": false,
"checkDigitApplicable": false,
"actualLength": 17,
"expectedLengths": [
17
],
"minLength": 17,
"invalidCharacters": [],
"algorithm": "ISO 3779 transliteration, weights 8-7-6-5-4-3-2-10-0-9-8-7-6-5-4-3-2, modulo 11; remainder 10 is written as X",
"scope": "The VIN is global; the position-9 check character is not. 49 CFR 565 requires one on every vehicle manufactured for sale in the United States and GB 16735 requires one in China, while no United Kingdom or European Union rule does. A VIN does not record which market it was built for, so this endpoint infers applicability from the ISO 3780 region block of the world manufacturer identifier alone and never marks a VIN outside the 1-5 and L blocks invalid on the check character.",
"notes": [
"The world manufacturer identifier 'WVW' begins with 'W', outside the ISO 3780 North American (1-5) and Chinese (L) region blocks, so position 9 is reported but never makes this VIN invalid. That is inferred from the WMI alone and is not the regulation: 49 CFR 565 requires a check digit on every vehicle manufactured for sale in the United States whatever its WMI, so a US-market European, Japanese or Korean vehicle does carry one. Read checkCharacterValid when you need the strict answer."
]
},
"meta": {
"endpoint": "check-digits",
"route": "/validate",
"params": {
"scheme": "vin",
"value": "WVWZZZ1JZXW000010",
"normalize": true,
"strict": false
},
"generatedAt": "2026-07-29T08:13:22.000Z"
}
} /api/check-digits/validate?scheme=gtin13&value=5901234123458 {
"data": {
"scheme": "gtin13",
"canonicalScheme": "gtin13",
"input": "5901234123458",
"normalized": "5901234123458",
"valid": false,
"reasons": [
"CHECK_CHARACTER_MISMATCH"
],
"payload": "590123412345",
"checkCharacter": "8",
"expectedCheckCharacter": "7",
"checkCharacterValid": false,
"checkDigitApplicable": true,
"actualLength": 13,
"expectedLengths": [
13
],
"minLength": 13,
"invalidCharacters": [],
"algorithm": "GS1 modulo-10: weights 3 and 1 alternating from the right, subtracted from the next multiple of ten",
"scope": "Global GS1 key, printed as an EAN-13 symbol.",
"notes": [
"The leading digits identify the GS1 Member Organisation that issued the company prefix. They are not a country of origin, a country of manufacture or a company address."
]
},
"meta": {
"endpoint": "check-digits",
"route": "/validate",
"params": {
"scheme": "gtin13",
"value": "5901234123458",
"normalize": true,
"strict": false
},
"generatedAt": "2026-07-29T08:13:22.000Z"
}
} /api/check-digits/validate?scheme=isbn13&value=5901234123457&strict=true {
"data": {
"scheme": "isbn13",
"canonicalScheme": "isbn13",
"input": "5901234123457",
"normalized": "5901234123457",
"valid": false,
"reasons": [
"STRICT_INVALID_PREFIX"
],
"payload": "590123412345",
"checkCharacter": "7",
"expectedCheckCharacter": "7",
"checkCharacterValid": true,
"checkDigitApplicable": true,
"actualLength": 13,
"expectedLengths": [
13
],
"minLength": 13,
"invalidCharacters": [],
"algorithm": "GS1 modulo-10 over the thirteen-digit Bookland EAN (weights 3 and 1 alternating from the right)",
"scope": "Global.",
"notes": [
"ISBN-13 values carry the Bookland prefix 978 or 979 (excluding 979-0). '590' is a valid GTIN-13 but not an ISBN."
]
},
"meta": {
"endpoint": "check-digits",
"route": "/validate",
"params": {
"scheme": "isbn13",
"value": "5901234123457",
"normalize": true,
"strict": true
},
"generatedAt": "2026-07-29T08:13:22.000Z"
}
} /api/check-digits/validate?scheme=isin&value=US0378331005 {
"data": {
"scheme": "isin",
"canonicalScheme": "isin",
"input": "US0378331005",
"normalized": "US0378331005",
"valid": true,
"reasons": [],
"payload": "US037833100",
"checkCharacter": "5",
"expectedCheckCharacter": "5",
"checkCharacterValid": true,
"checkDigitApplicable": true,
"actualLength": 12,
"expectedLengths": [
12
],
"minLength": 12,
"invalidCharacters": [],
"algorithm": "Letters expanded A=10…Z=35, then Luhn modulo-10 over the resulting decimal string",
"scope": "Global, for securities.",
"notes": []
},
"meta": {
"endpoint": "check-digits",
"route": "/validate",
"params": {
"scheme": "isin",
"value": "US0378331005",
"normalize": true,
"strict": false
},
"generatedAt": "2026-07-29T08:13:22.000Z"
}
}Takes the identifier without its check character(s) and returns both the character and the completed value. A malformed payload answers computable=false with reason codes.
| Parameter | Type | Default & allowed | Description |
|---|---|---|---|
scheme
required
| enum | allowed: luhn | gtin8 | gtin12 | gtin13 | gtin14 | upca | isbn10 | isbn13 | issn | ismn | imei | isin | lei | vin | npi | aba | iso7064-mod11-2 | iso7064-mod11-10 | iso7064-mod97-10 example: gtin13 | Identifier scheme to apply. 'upca' is an alias for 'gtin12'. 'npi' and 'aba' are United States schemes, and the 'vin' check character is only enforced where the world manufacturer identifier's ISO 3780 region block is North American (1-5) or Chinese (L). |
value
required
| string | allowed: 1 – 64 example: 590123412345 | The payload without its check character(s) — twelve digits for a GTIN-13, nine for an ISBN-10 or NPI, eighteen for a LEI. For a VIN, pass either the sixteen characters around position 9 or a full seventeen-character VIN whose position 9 is a placeholder. |
normalize | boolean | default: true example: true | Remove ASCII spaces and hyphens before checking. ASCII letters are uppercased either way, because every scheme's alphabet is uppercase-only. |
scheme enum required Identifier scheme to apply. 'upca' is an alias for 'gtin12'. 'npi' and 'aba' are United States schemes, and the 'vin' check character is only enforced where the world manufacturer identifier's ISO 3780 region block is North American (1-5) or Chinese (L).
value string required The payload without its check character(s) — twelve digits for a GTIN-13, nine for an ISBN-10 or NPI, eighteen for a LEI. For a VIN, pass either the sixteen characters around position 9 or a full seventeen-character VIN whose position 9 is a placeholder.
normalize boolean Remove ASCII spaces and hyphens before checking. ASCII letters are uppercased either way, because every scheme's alphabet is uppercase-only.
| Parameter | Type | Default & allowed | Description |
|---|---|---|---|
fields | list | example: scheme,canonicalScheme | Return only these fields (comma-separated). Mutually exclusive with 'exclude'. |
exclude | list | example: notes | Return all fields except these (comma-separated). |
pretty | boolean | default: false example: true | Pretty-print the JSON response. |
unwrap | boolean | default: false example: true | Drop the envelope: return the raw array/object without data/meta wrapper. |
fields list Return only these fields (comma-separated). Mutually exclusive with 'exclude'.
exclude list Return all fields except these (comma-separated).
pretty boolean Pretty-print the JSON response.
unwrap boolean Drop the envelope: return the raw array/object without data/meta wrapper.
| Field | Type | Description | Example |
|---|---|---|---|
scheme | string | Scheme id exactly as requested. | gtin13 |
canonicalScheme | string | Scheme actually applied — 'upca' resolves to 'gtin12'. | gtin13 |
input | string | The payload exactly as supplied. | 590123412345 |
payload nullable | string | Normalized payload used for the computation, or null when it was not computable. | 590123412345 |
checkCharacter nullable | string | The computed check character(s), or null when not computable. | 7 |
value nullable | string | The complete identifier, with the check character inserted where the scheme puts it (position 9 for a VIN, otherwise appended). Null when not computable. | 5901234123457 |
computable | boolean | Whether a check character could be computed at all. | true |
reasons | string[] | Stable ordered failure codes — EMPTY_AFTER_NORMALIZATION, INVALID_CHARACTERS, WRONG_PAYLOAD_LENGTH. Empty exactly when computable is true. | [] |
invalidCharacters | object[] | Every character outside the scheme's alphabet, in input order, as { index, character } with a zero-based index into the normalized value. When the length is wrong the check position cannot be located, so every character is tested against the scheme's full alphabet rather than the narrower check-position one. Empty when the alphabet check passed. | [{"index":4,"character":"#"}] |
expectedPayloadLengths | integer[] | Accepted payload lengths (total length minus the check characters). Empty for variable-length schemes; VIN accepts 16 or a full 17. | [12] |
actualPayloadLength | integer | Length of the normalized payload as supplied. | 12 |
checkDigitApplicable | boolean | Whether this endpoint would hold the computed character against the completed value. Always true except for a VIN whose world manufacturer identifier falls outside the ISO 3780 North American (1-5) and Chinese (L) region blocks — an inference from the WMI, not the regulation, so the value is still returned with the character in place and an explanatory note. | true |
algorithm | string | The algorithm applied, in one sentence. | GS1 modulo-10: weights 3 and 1 alternating from the right, subtracted from the next multiple of ten |
scope | string | Where this scheme and its check character actually apply. | Global GS1 key, printed as an EAN-13 symbol. |
notes | string[] | Situational explanations, such as a VIN placeholder form or the GS1 prefix caveat. | [] |
scheme string Scheme id exactly as requested.
example: gtin13
canonicalScheme string Scheme actually applied — 'upca' resolves to 'gtin12'.
example: gtin13
input string The payload exactly as supplied.
example: 590123412345
payload string nullable Normalized payload used for the computation, or null when it was not computable.
example: 590123412345
checkCharacter string nullable The computed check character(s), or null when not computable.
example: 7
value string nullable The complete identifier, with the check character inserted where the scheme puts it (position 9 for a VIN, otherwise appended). Null when not computable.
example: 5901234123457
computable boolean Whether a check character could be computed at all.
example: true
reasons string[] Stable ordered failure codes — EMPTY_AFTER_NORMALIZATION, INVALID_CHARACTERS, WRONG_PAYLOAD_LENGTH. Empty exactly when computable is true.
example: []
invalidCharacters object[] Every character outside the scheme's alphabet, in input order, as { index, character } with a zero-based index into the normalized value. When the length is wrong the check position cannot be located, so every character is tested against the scheme's full alphabet rather than the narrower check-position one. Empty when the alphabet check passed.
example: [{"index":4,"character":"#"}]
expectedPayloadLengths integer[] Accepted payload lengths (total length minus the check characters). Empty for variable-length schemes; VIN accepts 16 or a full 17.
example: [12]
actualPayloadLength integer Length of the normalized payload as supplied.
example: 12
checkDigitApplicable boolean Whether this endpoint would hold the computed character against the completed value. Always true except for a VIN whose world manufacturer identifier falls outside the ISO 3780 North American (1-5) and Chinese (L) region blocks — an inference from the WMI, not the regulation, so the value is still returned with the character in place and an explanatory note.
example: true
algorithm string The algorithm applied, in one sentence.
example: GS1 modulo-10: weights 3 and 1 alternating from the right, subtracted from the next multiple of ten
scope string Where this scheme and its check character actually apply.
example: Global GS1 key, printed as an EAN-13 symbol.
notes string[] Situational explanations, such as a VIN placeholder form or the GS1 prefix caveat.
example: []
/api/check-digits/compute?scheme=gtin13&value=590123412345 {
"data": {
"scheme": "gtin13",
"canonicalScheme": "gtin13",
"input": "590123412345",
"payload": "590123412345",
"checkCharacter": "7",
"value": "5901234123457",
"computable": true,
"reasons": [],
"invalidCharacters": [],
"expectedPayloadLengths": [
12
],
"actualPayloadLength": 12,
"checkDigitApplicable": true,
"algorithm": "GS1 modulo-10: weights 3 and 1 alternating from the right, subtracted from the next multiple of ten",
"scope": "Global GS1 key, printed as an EAN-13 symbol.",
"notes": [
"The leading digits identify the GS1 Member Organisation that issued the company prefix. They are not a country of origin, a country of manufacture or a company address."
]
},
"meta": {
"endpoint": "check-digits",
"route": "/compute",
"params": {
"scheme": "gtin13",
"value": "590123412345",
"normalize": true
},
"generatedAt": "2026-07-29T08:13:22.000Z"
}
} /api/check-digits/compute?scheme=isbn10&value=043942089 {
"data": {
"scheme": "isbn10",
"canonicalScheme": "isbn10",
"input": "043942089",
"payload": "043942089",
"checkCharacter": "X",
"value": "043942089X",
"computable": true,
"reasons": [],
"invalidCharacters": [],
"expectedPayloadLengths": [
9
],
"actualPayloadLength": 9,
"checkDigitApplicable": true,
"algorithm": "Modulo-11 with descending weights 10…2; remainder 10 is written as X",
"scope": "Global. Withdrawn for new assignments in 2007 but still present in legacy catalogues; every ISBN-10 has an equivalent 978-prefixed ISBN-13.",
"notes": []
},
"meta": {
"endpoint": "check-digits",
"route": "/compute",
"params": {
"scheme": "isbn10",
"value": "043942089",
"normalize": true
},
"generatedAt": "2026-07-29T08:13:22.000Z"
}
} /api/check-digits/compute?scheme=vin&value=1HGCM8263A004352 {
"data": {
"scheme": "vin",
"canonicalScheme": "vin",
"input": "1HGCM8263A004352",
"payload": "1HGCM8263A004352",
"checkCharacter": "3",
"value": "1HGCM82633A004352",
"computable": true,
"reasons": [],
"invalidCharacters": [],
"expectedPayloadLengths": [
16,
17
],
"actualPayloadLength": 16,
"checkDigitApplicable": true,
"algorithm": "ISO 3779 transliteration, weights 8-7-6-5-4-3-2-10-0-9-8-7-6-5-4-3-2, modulo 11; remainder 10 is written as X",
"scope": "The VIN is global; the position-9 check character is not. 49 CFR 565 requires one on every vehicle manufactured for sale in the United States and GB 16735 requires one in China, while no United Kingdom or European Union rule does. A VIN does not record which market it was built for, so this endpoint infers applicability from the ISO 3780 region block of the world manufacturer identifier alone and never marks a VIN outside the 1-5 and L blocks invalid on the check character.",
"notes": [
"The world manufacturer identifier '1HG' begins with '1', the ISO 3780 North American region block, so this VIN is treated as one 49 CFR 565 covers and the position-9 check character is required."
]
},
"meta": {
"endpoint": "check-digits",
"route": "/compute",
"params": {
"scheme": "vin",
"value": "1HGCM8263A004352",
"normalize": true
},
"generatedAt": "2026-07-29T08:13:22.000Z"
}
} /api/check-digits/compute?scheme=lei&value=L3I9ZG2KFGXZ61BMYR {
"data": {
"scheme": "lei",
"canonicalScheme": "lei",
"input": "L3I9ZG2KFGXZ61BMYR",
"payload": "L3I9ZG2KFGXZ61BMYR",
"checkCharacter": "72",
"value": "L3I9ZG2KFGXZ61BMYR72",
"computable": true,
"reasons": [],
"invalidCharacters": [],
"expectedPayloadLengths": [
18
],
"actualPayloadLength": 18,
"checkDigitApplicable": true,
"algorithm": "ISO/IEC 7064 MOD 97-10 over the twenty characters with letters expanded A=10…Z=35; a valid LEI leaves remainder 1",
"scope": "Global, for legal entities in financial transactions.",
"notes": [
"ISO 17442 reserves characters 5 and 6 as '00', but some registered LEIs do not follow that convention, so this endpoint does not treat it as a validity rule."
]
},
"meta": {
"endpoint": "check-digits",
"route": "/compute",
"params": {
"scheme": "lei",
"value": "L3I9ZG2KFGXZ61BMYR",
"normalize": true
},
"generatedAt": "2026-07-29T08:13:22.000Z"
}
} /api/check-digits/compute?scheme=npi&value=123456789 {
"data": {
"scheme": "npi",
"canonicalScheme": "npi",
"input": "123456789",
"payload": "123456789",
"checkCharacter": "3",
"value": "1234567893",
"computable": true,
"reasons": [],
"invalidCharacters": [],
"expectedPayloadLengths": [
9
],
"actualPayloadLength": 9,
"checkDigitApplicable": true,
"algorithm": "Luhn modulo-10 over 80840 followed by the nine-digit payload",
"scope": "United States only. The National Provider Identifier is issued by CMS for US health care providers; it has no meaning elsewhere.",
"notes": []
},
"meta": {
"endpoint": "check-digits",
"route": "/compute",
"params": {
"scheme": "npi",
"value": "123456789",
"normalize": true
},
"generatedAt": "2026-07-29T08:13:22.000Z"
}
}Detects the source form from its length, verifies its own check character, then re-expresses it as the target and recomputes the check character.
| Parameter | Type | Default & allowed | Description |
|---|---|---|---|
value
required
| string | allowed: 1 – 64 example: 036000291452 | Source identifier: a GTIN-8, ISBN-10, GTIN-12/UPC-A, GTIN-13/ISBN-13 or GTIN-14. Spaces and hyphens are always removed. Its own check character must be correct. |
to
required
| enum | allowed: gtin13 | gtin14 | upca | isbn10 | isbn13 example: gtin13 | Target form. Conversions that do not exist — a GTIN-14 above indicator 0, a GTIN-13 without a leading zero to UPC-A, a 979-prefixed ISBN-13 to ISBN-10 — return a 400 explaining why. |
value string required Source identifier: a GTIN-8, ISBN-10, GTIN-12/UPC-A, GTIN-13/ISBN-13 or GTIN-14. Spaces and hyphens are always removed. Its own check character must be correct.
to enum required Target form. Conversions that do not exist — a GTIN-14 above indicator 0, a GTIN-13 without a leading zero to UPC-A, a 979-prefixed ISBN-13 to ISBN-10 — return a 400 explaining why.
| Parameter | Type | Default & allowed | Description |
|---|---|---|---|
fields | list | example: input,normalized | Return only these fields (comma-separated). Mutually exclusive with 'exclude'. |
exclude | list | example: notes | Return all fields except these (comma-separated). |
pretty | boolean | default: false example: true | Pretty-print the JSON response. |
unwrap | boolean | default: false example: true | Drop the envelope: return the raw array/object without data/meta wrapper. |
fields list Return only these fields (comma-separated). Mutually exclusive with 'exclude'.
exclude list Return all fields except these (comma-separated).
pretty boolean Pretty-print the JSON response.
unwrap boolean Drop the envelope: return the raw array/object without data/meta wrapper.
| Field | Type | Description | Example |
|---|---|---|---|
input | string | The source value exactly as supplied. | 036000291452 |
normalized | string | Uppercased source with ASCII spaces and hyphens removed. | 036000291452 |
sourceForm | string | Detected source form: gtin8, isbn10, gtin12, gtin13 or gtin14. | gtin12 |
sourceCheckCharacter | string | The source's own (verified) check character. | 2 |
to | string | Requested target form. | gtin13 |
value | string | The converted identifier, with its check character recomputed for the target form. | 0036000291452 |
checkCharacter | string | Check character of the converted value. | 2 |
checkCharacterChanged | boolean | Whether the converted value's check character literally differs from the source's. Zero-padding between GTIN forms never changes it, because GS1 weights run from the right. An ISBN-10 ↔ ISBN-13 conversion always recomputes it under the other algorithm, but about one such conversion in ten lands on the same character and so reports false. | false |
notes | string[] | What the conversion did and any caveat that applies to it. | [] |
input string The source value exactly as supplied.
example: 036000291452
normalized string Uppercased source with ASCII spaces and hyphens removed.
example: 036000291452
sourceForm string Detected source form: gtin8, isbn10, gtin12, gtin13 or gtin14.
example: gtin12
sourceCheckCharacter string The source's own (verified) check character.
example: 2
to string Requested target form.
example: gtin13
value string The converted identifier, with its check character recomputed for the target form.
example: 0036000291452
checkCharacter string Check character of the converted value.
example: 2
checkCharacterChanged boolean Whether the converted value's check character literally differs from the source's. Zero-padding between GTIN forms never changes it, because GS1 weights run from the right. An ISBN-10 ↔ ISBN-13 conversion always recomputes it under the other algorithm, but about one such conversion in ten lands on the same character and so reports false.
example: false
notes string[] What the conversion did and any caveat that applies to it.
example: []
/api/check-digits/convert?value=036000291452&to=gtin13 {
"data": {
"input": "036000291452",
"normalized": "036000291452",
"sourceForm": "gtin12",
"sourceCheckCharacter": "2",
"to": "gtin13",
"value": "0036000291452",
"checkCharacter": "2",
"checkCharacterChanged": false,
"notes": [
"GS1 represents a shorter GTIN in a longer data field by right-justifying it with leading zeros. The check digit is unchanged because GS1 weights are assigned from the right."
]
},
"meta": {
"endpoint": "check-digits",
"route": "/convert",
"params": {
"value": "036000291452",
"to": "gtin13"
},
"generatedAt": "2026-07-29T08:13:22.000Z"
}
} /api/check-digits/convert?value=9780306406157&to=isbn10 {
"data": {
"input": "9780306406157",
"normalized": "9780306406157",
"sourceForm": "gtin13",
"sourceCheckCharacter": "7",
"to": "isbn10",
"value": "0306406152",
"checkCharacter": "2",
"checkCharacterChanged": true,
"notes": [
"This GTIN-13 carries a Bookland prefix, so it is also an ISBN-13.",
"The 978 prefix is dropped and the modulo-11 check character (0-9 or X) is recomputed from the remaining nine digits."
]
},
"meta": {
"endpoint": "check-digits",
"route": "/convert",
"params": {
"value": "9780306406157",
"to": "isbn10"
},
"generatedAt": "2026-07-29T08:13:22.000Z"
}
} /api/check-digits/convert?value=0-306-40615-2&to=isbn13 {
"data": {
"input": "0-306-40615-2",
"normalized": "0306406152",
"sourceForm": "isbn10",
"sourceCheckCharacter": "2",
"to": "isbn13",
"value": "9780306406157",
"checkCharacter": "7",
"checkCharacterChanged": true,
"notes": [
"ISBN-10 uses a modulo-11 check character (0-9 or X) while ISBN-13 and the GTIN forms use the GS1 modulo-10 check digit, so the check character is recomputed rather than carried over."
]
},
"meta": {
"endpoint": "check-digits",
"route": "/convert",
"params": {
"value": "0-306-40615-2",
"to": "isbn13"
},
"generatedAt": "2026-07-29T08:13:22.000Z"
}
} /api/check-digits/convert?value=5901234123457&to=gtin14 {
"data": {
"input": "5901234123457",
"normalized": "5901234123457",
"sourceForm": "gtin13",
"sourceCheckCharacter": "7",
"to": "gtin14",
"value": "05901234123457",
"checkCharacter": "7",
"checkCharacterChanged": false,
"notes": [
"GS1 represents a shorter GTIN in a longer data field by right-justifying it with leading zeros. The check digit is unchanged because GS1 weights are assigned from the right.",
"Packaging indicator 0 identifies the base trade item. A GTIN-14 built with indicator 0 keeps the source check digit; indicators 1-9 describe higher packaging levels and are assigned by the brand owner, not derived."
]
},
"meta": {
"endpoint": "check-digits",
"route": "/convert",
"params": {
"value": "5901234123457",
"to": "gtin14"
},
"generatedAt": "2026-07-29T08:13:22.000Z"
}
}Nineteen check-character schemes, each implemented straight from its published algorithm and each reporting which rule failed, not just a boolean. /validate checks an identifier, /compute returns the character a payload is missing, /convert moves between equivalent GTIN and ISBN forms, and the root route documents every scheme's algorithm, alphabet, length rules and error-detection limits.
A valid check digit means well-formed — nothing more. It does not mean the identifier was issued, assigned, registered, listed, enumerated or is tradeable. This endpoint holds no product catalogue, securities master, vehicle history, device database or provider registry, and it makes no network calls, so it cannot tell you whether a number belongs to anything real.
Regional scope matters, and we say exactly how far we can see. The VIN check character at position 9 is required by 49 CFR 565 on vehicles manufactured for sale in the United States and by GB 16735 in China; no United Kingdom or European Union rule requires one. A VIN does not record which market it was built for, so scheme=vin reads the ISO 3780 region block of the world manufacturer identifier and returns checkDigitApplicable: false outside the 1-5 and L blocks, where a position-9 mismatch is reported in checkCharacterValid but never makes valid false. That is an inference, not the regulation: a US-market BMW, Toyota or Hyundai carries a mandatory check digit under a W, J or K WMI, so checkDigitApplicable: false means "not determinable from the VIN alone" — read checkCharacterValid when you need the strict answer. npi and aba are United States schemes and say so in their own scope field.
Error detection is not universal, so each scheme states its own limits. Mod-10 systems cannot see every transposition: Luhn (and therefore IMEI, NPI and the last step of ISIN) misses the 09 ↔ 90 swap, while the GS1 and ABA weightings miss adjacent digits five apart. The modulus-11 and modulus-97 systems — ISBN-10, ISSN, ISO 7064 MOD 11-2 and MOD 97-10 — catch every adjacent transposition; ISO 7064 MOD 11,10 misses a small minority, and ISIN misses every adjacent letter-letter swap, the country prefix included. ISIN, LEI and VIN do not even catch every single-character substitution: VIN's transliteration table is many-to-one, so A and J are indistinguishable to the check character, while ISIN and LEI expand letters into two digits, so a letter-for-digit substitution changes the arithmetic's shape rather than just one term. Every scheme record carries detectsAllSingleCharacterErrors and detectsAllAdjacentTranspositions, plus a plain-English description of exactly what slips through when something does.
Errors are structured, not thrown. A wrong length or an out-of-alphabet character produces a valid: false record with ordered reasons codes and an invalidCharacters list naming each offending character and its index. Beyond the platform's ordinary parameter validation — a missing value, a value over 64 characters, an unrecognized scheme or to — the only 400 this endpoint raises is a /convert request that is genuinely impossible.
strict=false (the default) checks alphabet, length and check character only. strict=true adds the specification's structural rules where they exist: the ISBN-13 Bookland prefix (978, or 979 other than 979-0, which is the ISMN prefix), the ISMN 9790 prefix, the two-letter ISIN prefix, the North-American VIN model-year code and the allocated Federal Reserve routing symbols. For the fourteen schemes with no further rules, strict=true returns a warning saying so rather than pretending to do more.
Deliberate exclusions. National identity numbers are out of scope entirely. GS1 prefix → company or country lookup is out of scope: the table is not ours to redistribute, and "prefix equals country of origin" is false in any case — the leading digits identify the GS1 Member Organisation that issued the company prefix. ISBN hyphenation is out of scope because the ISBN range message is not redistributable. IBAN national layouts stay in the ibans endpoint; this one owns the generic ISO 7064 MOD 97-10 algorithm. GS1 and ISO standards texts are paywalled: we implement and cite the published algorithms, we do not reproduce the standards.
Call /api/check-digits/validate?scheme=imei&value=490154203237518. It runs the Luhn check that 3GPP TS 23.003 defines over the fourteen TAC and serial digits. A pass means the fifteen digits are well formed — it does not mean the device exists or that the Type Allocation Code was ever issued.
GS1 weights the data digits 3 and 1 alternately from the right, sums them and subtracts the total from the next multiple of ten. /api/check-digits/compute?scheme=gtin13&value=590123412345 returns the digit, and the identical rule covers GTIN-8, GTIN-12/UPC-A and GTIN-14.
No. The leading digits identify the GS1 Member Organisation that issued the company prefix — not where a product was made, nor where the company is based. A firm can join GS1 in one country and manufacture anywhere, so this endpoint deliberately ships no prefix-to-country table.
Because position 9 is a check character only where a regulator requires it — 49 CFR 565 in the United States, GB 16735 in China — and no UK or EU rule does. A VIN does not record its market, so this endpoint reads the ISO 3780 region block of the world manufacturer identifier: outside the 1-5 and L blocks it returns checkDigitApplicable: false and never lets a position-9 mismatch make valid false. That is an inference, not the regulation, so read checkCharacterValid for the strict answer — a US-market BMW or Toyota does carry a mandatory check digit.
Only when the prefix is 978. /api/check-digits/convert?value=9780306406157&to=isbn10 drops the prefix and recomputes the modulo-11 character. A 979-prefixed ISBN-13 has no ISBN-10 at all and returns a 400 that says exactly that.
Every scheme here catches all single-character substitutions except ISIN, LEI and VIN, where expanding or transliterating letters into digits either collapses characters onto the same contribution (VIN) or changes the length of the string being weighed (ISIN, LEI — so 0 typed as O can slip through). Adjacent transpositions vary: Luhn misses only 09 ↔ 90, the GS1 and ABA mod-10 weightings miss digits five apart, ISO 7064 MOD 11,10 misses a small minority, ISIN misses every letter-letter swap, and the modulus-11 and modulus-97 systems miss none. Each scheme record spells out its own limits.
Clearly-fake test credit cards — Luhn-valid numbers with correct Visa, Mastercard, Amex and Discover prefixes, future expiry and matching CVV.
Generate synthetic IBAN-shaped values for 20 countries with matching length, broad BBAN character classes and international MOD-97, or inspect the same checks.
Fake e-commerce products with category-themed names, prices in real currencies (whole yen for JPY), valid EAN-13 barcodes, SKUs, ratings and image URLs.
Fake books with genre-flavored titles, checksum-valid ISBN-13s, authors, page counts and invented publishers. Filter by genre and page range.
Coherent fake vehicles: real models per make, era-correct years, standards-valid VINs (ISO 3779 check digit) — filter by make, body type, fuel and year.
Bounded SemVer 2.0.0 parsing, precedence comparison and major/minor/patch bumps, with explicit size limits instead of precision loss.