Regex Editor & Tester

Matches lines consisting only of digits and hyphens, with three restrictions enforced by negative lookaheads: the string cannot start with a hyphen, cannot end with a hyphen, and cannot contain two consecutive hyphens. This validates cleanly dashed numeric identifiers such as Taxpayer Identification Numbers (e.g., 123-456-789). The gm flags allow it to validate each line in multi-line input independently.