Search / com.gumballtools/check-digit
protogridR0· no sign-inValidates IBAN/ISBN/EAN/Luhn checksums and finds the one wrong digit
v0.1.0 · active · repository · website · descriptor JSON · versions
{
"mcpServers": {
"check-digit": {
"type": "http",
"url": "https://check-digit.gumballtools.com/api/mcp"
}
}
}claude mcp add --transport http check-digit https://check-digit.gumballtools.com/api/mcp[mcp_servers.check-digit]
url = "https://check-digit.gumballtools.com/api/mcp"
{
"$schema": "https://opencode.ai/config.json",
"mcp": {
"check-digit": {
"type": "remote",
"url": "https://check-digit.gumballtools.com/api/mcp",
"enabled": true
}
}
}{
"mcpServers": {
"check-digit": {
"type": "http",
"url": "https://check-digit.gumballtools.com/api/mcp"
}
},
"deeplink": "cursor://anysphere.cursor-deeplink/mcp/install?name=check-digit&config=eyJ0eXBlIjoiaHR0cCIsInVybCI6Imh0dHBzOi8vY2hlY2stZGlnaXQuZ3VtYmFsbHRvb2xzLmNvbS9hcGkvbWNwIn0%3D"
}{
"servers": {
"check-digit": {
"type": "http",
"url": "https://check-digit.gumballtools.com/api/mcp"
}
}
}{
"mcpServers": {
"check-digit": {
"httpUrl": "https://check-digit.gumballtools.com/api/mcp"
}
}
}extensions:
"check-digit":
enabled: true
name: "check-digit"
type: streamable_http
uri: "https://check-digit.gumballtools.com/api/mcp"
timeout: 300
protocol.modernsupports 2026-07-28 (server/discover)protocol.statelessanswers without a sessionprotocol.transportstreamable HTTPprotocol.list_ttltools/list declares ttlMs 0, so clients re-fetch it on every useauth.prm, auth.as_metadata, auth.cimdno remote uses OAuthauth.secret_in_urlno templated URLtools.descriptionsevery tool has a descriptiontools.description_length1 tools have descriptions over 1,024 characters, which crowds the contexttools.schemasevery tool has an object input schematools.annotations1 of 1 tools declare readOnlyHint or destructiveHinttools.directory_hintsno tool declares all four of readOnlyHint, destructiveHint, idempotentHint and openWorldHint; missing: run (destructiveHint, idempotentHint)tools.token_costabout 660 tokens to load every tooltools.api_dumptools are not a one-to-one API dumpstability.changesno tool changes in 30 daysstability.rug_pullno tool changed its meaning under the same namedeps.known_vulns, deps.mcp_sdk_version, deps.resolvableno npm or PyPI packageNo tool definition changes recorded. A server's first observation is its baseline; later probes record what changes.
Checks run on what our credential-free, read-only probes observe; tools are never called and no code audit is performed. How it is computed.
+repository +dns-namespace +website +reachable +uptime-100% ~updated-45d-ago -duplicate-repo(16 names)
Derived from observable signals (official registry feed and our own credential-free probes); no code audit performed. How it is computed.
| remote | auth | reachable | uptime 30d | p50 | protocol | last ok |
|---|---|---|---|---|---|---|
https://check-digit.gumballtools.com/api/mcp streamable-http | none | yes | 100% | 904 ms | 2026-07-28 | 2026-10-20 |
runread-only | Validate the check digit(s) on an IBAN, ISBN-10, ISBN-13, EAN-13, UPC-A, or Luhn-checked card number, and when it fails, try to say which digit is wrong. Use this instead of computing the checksum yourself. Mod-97 arithmetic on a rearranged 15-34 character IBAN, or a weighted sum mod 10/11 over 10-19 digits, is exactly the kind of long deterministic calculation language models get wrong silently and confidently — there is no way for a reader to tell a fabricated "valid" from a real one without redoing the math. This tool actually redoes the math, and when the checksum fails, searches for the single adjacent-digit swap or single-character substitution that would repair it, because a transposed pair is the most common real cause of a bounced payment or a mistyped barcode. IMPORTANT, and easy to get wrong: for ISBN-13/EAN-13/UPC-A and Luhn, the digit alphabet (0-9) almost exactly spans the checksum's modulus, so a failing check usually admits MANY equally valid single-digit substitutions — the math genuinely cannot narrow it to one digit unless the error was an adjacent transposition. When that happens, the response reports the full candidate list rather than picking one; treat that as the honest answer, not a failure to find it. IBAN (mod 97) is the exception and usually does localize to one digit. Inputs: `input` (the number; spaces and hyphens are stripped automatically) and `format`, one of iban | isbn10 | isbn13 | ean13 | upca | luhn — required, never auto-detected, because the same digit string can be validly checked under more than one format with different results. Refuses rather than guesses: an IBAN country code not in the ISO 13616 length registry, the wrong length for a declared format, or characters outside the format's alphabet (e.g. a letter in a card number). A passing checksum is a syntax check only — it does not confirm an IBAN names an open account, an ISBN is a real book, or a card is active or unstolen. |
Schemas: list_tools.
15 other active names share this repository (showing 10): com.crontoenglish/cron-translator, com.gumballtools/amortize, com.gumballtools/body-metrics, com.gumballtools/color-companion, com.gumballtools/due-date, com.gumballtools/equation-steps, com.gumballtools/iso-week, com.gumballtools/json-to-types, com.gumballtools/payload-validator, com.gumballtools/penny-rounding
And 8 more from this publisher.
{
"name": "com.gumballtools/check-digit",
"title": "Check Digit Validator",
"$schema": "https://static.modelcontextprotocol.io/schemas/2025-12-11/server.schema.json",
"remotes": [
{
"url": "https://check-digit.gumballtools.com/api/mcp",
"type": "streamable-http"
}
],
"version": "0.1.0",
"repository": {
"url": "https://github.com/bwalvoord/gumball",
"source": "github"
},
"websiteUrl": "https://check-digit.gumballtools.com",
"description": "Validates IBAN/ISBN/EAN/Luhn checksums and finds the one wrong digit"
}