Regex Tester & Validator

Matches a standalone 9-digit number that starts with 5, such as purchase order numbers or specific account/ID formats. The boundary groups (^|\D) and ($|\D) ensure the digits are not part of a longer number, while \b prevents a word character (like a letter) from directly preceding it. With global and multiline flags, it's ideal for scanning logs, invoices, or line-based documents for these identifiers.