# Services from checkdigit.openverbs.com on Zero

> checkdigit.openverbs.com serves 5 paid API services for AI agents, indexed by Zero. Each is callable per call with payment handled by Zero.

Canonical page: https://www.zero.xyz/host/checkdigit.openverbs.com
Live health (JSON, refreshed every minute): https://www.zero.xyz/host/checkdigit.openverbs.com/health.json

## Services

- [IMEI Luhn Check Digit Validator](https://www.zero.xyz/c/imei-luhn-check-digit-validator-e1026f97/llms.txt): $0.002/call via x402. Validates a 15-digit mobile device IMEI number by verifying its Luhn (mod-10) check digit.
- [ISBN Validator (ISBN-10 and ISBN-13)](https://www.zero.xyz/c/isbn-validator-isbn-10-and-isbn-13-f885cefd/llms.txt): $0.002/call via x402. Validates an ISBN-10 or ISBN-13 book number using mod-11 or GTIN mod-10 checksum algorithms respectively, with automatic scheme selection based on digit length.
- [GTIN/EAN Barcode Check Digit Validator](https://www.zero.xyz/c/gtin-ean-barcode-check-digit-validator-7ad1f398/llms.txt): $0.002/call via x402. Validates EAN-8, UPC-A (12-digit), EAN-13, or GTIN-14 barcode numbers using the standard mod-10 check digit algorithm.
- [ABA Routing Number Checksum Validator](https://www.zero.xyz/c/aba-routing-number-checksum-validator-129fe232/llms.txt): $0.002/call via x402. Validates a 9-digit US ABA bank routing number using the weighted (3,7,1) mod-10 checksum algorithm
- [Luhn Algorithm Validator (checkdigit.openverbs.com)](https://www.zero.xyz/c/luhn-algorithm-validator-checkdigit-openverbs-com-a1296cb5/llms.txt): $0.002/call via x402. Validates any digit string against the Luhn (mod-10) checksum algorithm, returning whether the number has a valid check digit.

Status and success rate cover calls made through Zero and Zero's own probes. Third-party monitors may report differently.

- [Zero catalog index](https://www.zero.xyz/llms.txt)