Regex Tester & Validator

This regular expression matches a specific phone number format consisting of a single digit (often used for a country code like '1' for North America), followed by three digits, another three digits, and a final four digits. Each of these numeric groups must be strictly separated by a hyphen, matching patterns like "1-800-123-4567". It is highly rigid and only allows this exact sequence, making it unsuitable for numbers with spaces, parentheses, or missing hyphens.