Never use naive regular expressions to validate international phone numbers; use Google's libphonenumber standard to format numbers into canonical E.164.
Global phone numbers follow complex national numbering plans with varying digit lengths, trunk prefixes (such as the leading '0' in the UK or '01' in Germany), and area code formats. Naive regex checks cause massive user rejection. This guide details international number parsing best practices.
1 The E.164 Canonical Standard
The International Telecommunication Union (ITU) E.164 standard mandates:
- Prefix: Leading '+' character.
- Country Code: 1 to 3 digits (e.g. '1' for US/Canada, '44' for UK, '49' for Germany).
- Subscriber Number: Maximum 15 total digits with no spaces, dashes, or punctuation.
Always store and transmit numbers in canonical E.164 format.
Frequently Asked Questions • QA Automation & Testing
Yes. SMSRiver provides a free, instant Phone Number Formatter tool (/tools/phone-number-formatter/) that normalizes raw input into E.164, RFC 3966, and national formats.