Luhn check API: validate card and IMEI numbers, compute check digit

$0.01 per call · failed calls are never charged · no account or subscription: pay per call with a card key or USDC

Luhn check: whether a card number or other ID passes the Luhn (mod 10) algorithm used by card numbers, IMEI numbers and many IDs, and compute the check digit to append. Only the format is checked; nothing is looked up. Use to catch typos in card or ID numbers.

When to use it

Run it free (25 free calls) Buy credits by card (from $1) Example result (JSON)

Try it with your own inputs

Digits, spaces and hyphens allowed

Uses one of your 25 free calls. Nothing is charged, and a call that fails is not counted.

Inputs

NameTypeDescription
number (required)stringDigits, spaces and hyphens allowed

Request

Over HTTP, with a card key from /credits:

curl -H "Authorization: Bearer adt_…" "https://tools.funwords.eu/validate/luhn?number=79927398713"

Or one of your 25 free calls, no key:

curl "https://tools.funwords.eu/validate/luhn?number=79927398713&trial=1"

Without a key, the same URL answers 402 Payment Required with x402 and MPP terms, so an agent with a wallet pays per call in USDC (Base, Polygon, Arbitrum or Solana over x402; Base or Tempo over MPP) and retries.

Example result

{
  "digits": "79927398713",
  "valid": true,
  "checkDigitForPrefix": 3
}

From an AI agent (MCP)

Add the MCP server to Claude, Cursor or any MCP client. This tool is validate_luhn, and the first 25 successful calls are free:

https://tools.funwords.eu/mcp

Questions

Does it check whether the card exists?

No. Only the format (mod 10) is checked; nothing is looked up.

How do I pay?

Each successful call costs $0.01; failed calls are not charged. The first 25 calls are free. Then pay with card credits (from $1; the key goes in an Authorization header or, for clients that can only fetch a URL, as api_key= in the URL) or per call in USDC over x402 or MPP. No account is needed.

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