Phone number validation is harder than you think (a libphonenumber crash course)

A regex will not validate phone numbers correctly. I promise. Numbering plans vary by country, mobile vs landline prefixes differ, and some countries have variable-length numbers. Google's libphonenumber (the library that powers Android's dialer) is the only sane way to do this client- or server-side.

import parsePhoneNumberFromString from "libphonenumber-js";

const parsed = parsePhoneNumberFromString("[phone]");
console.log(parsed.isValid());          // true
console.log(parsed.country);            // "DE"
console.log(parsed.formatInternational()); // "[phone]"

Two gotchas that catch people out: numbers without a country code need a defaultCountry hint or parsing will silently fail, and "valid" only means "matches the numbering plan" — it says nothing about whether the number is currently assigned to someone.

For a stateless HTTP version of this (useful if your stack isn't JS, or you don't want the dependency), I built it as one of the endpoints on Validate — same libphonenumber-js under the hood, just over JSON. Same account also covers QR API and Currency API.