How to Validate CUSIP and ISIN Security Identifiers

How to Validate CUSIP and ISIN Security Identifiers Every security traded on US and international markets has a unique identifier. In the United States, that identifier is a CUSIP (Committee on Uniform Securities Identification Procedures). Internationally, it is an ISIN (International Securities Identification Number). Both include a check digit that can be validated algorithmically -- no database lookup required. If you are building a trading platform, portfolio tracker, reconciliation system, or any application that handles security identifiers, validating these numbers at the point of entry catches data errors before they propagate through your system. What is a CUSIP A CUSIP is a 9-character identifier assigned to securities traded in the United States and Canada. It has three parts: Characters 1-6 : Issuer code (identifies the company or entity) Characters 7-8 : Issue number (identifies the specific security from that issuer) Character 9 : Check digit Characters can be digits (0-