International Phone Validation: Handling Global Number Formats

International phone validation requires understanding diverse numbering plans, cultural conventions, and regulatory requirements. Building globally compatible validation systems demands comprehensive knowledge of regional variations and standards.

Cleariflow Phone Validation API scope: Our Phone Validation API performs structural validation via Google libphonenumber, E.164 normalization, line type, and optional carrier/location metadata (mainly US/CA). It does not perform HLR/MNP lookups, line-status checks, or subscriber verification. Advanced topics below describe patterns you can combine with the API in a larger stack.

Overview

Phone number formats vary dramatically by country, requiring country-specific validation rules. ITU-T E.164 provides the global framework, but implementation requires handling regional numbering plans, formatting conventions, and carrier-specific patterns.

E.164 Standard

International standard for phone numbering.

interface E164Number {
  countryCode: string // 1-3 digits
  nationalNumber: string // Up to 15 total digits
  formatted: string
}

function parseE164(number: string): E164Number {
  const cleaned = number.replace(/D/g, '')
  const countryCode = cleaned.slice(0, 1) // Simplified
  const nationalNumber = cleaned.slice(1)
  
  return {
    countryCode,
    nationalNumber,
    formatted: `+${countryCode} ${nationalNumber}`
  }
}

Country-Specific Rules

Different countries have different validation rules. In production, prefer libphonenumber (as used by Cleariflow) over hand-maintained regex tables — numbering plans change frequently.

interface CountryRules {
  code: string
  minLength: number
  maxLength: number
  pattern: RegExp
  format: string
}

const COUNTRY_RULES: Record<string, CountryRules> = {
  'US': {
    code: '+1',
    minLength: 10,
    maxLength: 10,
    pattern: /^[2-9]d{2}[2-9]d{6}$/,
    format: '(XXX) XXX-XXXX'
  },
  'UK': {
    code: '+44',
    minLength: 10,
    maxLength: 10,
    pattern: /^[1-9]d{9}$/,
    format: 'XXXX XXX XXXX'
  },
  'DE': {
    code: '+49',
    minLength: 10,
    maxLength: 11,
    pattern: /^[1-9]d{9,10}$/,
    format: 'XXX XXXXXXXX'
  }
}

Number Formatting

Format numbers according to local conventions.

class PhoneFormatter {
  format(number: string, country: string): string {
    const rules = COUNTRY_RULES[country]
    if (!rules) return number
    
    const cleaned = number.replace(/D/g, '')
    let formatted = rules.code + ' '
    
    // Apply country-specific formatting
    // Simplified implementation
    return formatted + cleaned
  }
}

Validation Implementation

Validate phone numbers globally.

class InternationalPhoneValidator {
  validate(number: string, expectedCountry?: string): {
    valid: boolean
    country: string
    formatted: string
  } {
    const cleaned = number.replace(/D/g, '')
    
    for (const [country, rules] of Object.entries(COUNTRY_RULES)) {
      if (expectedCountry && country !== expectedCountry) continue
      
      const nationalNumber = cleaned.replace(rules.code.replace('+', ''), '')
      
      if (nationalNumber.length >= rules.minLength && 
          nationalNumber.length <= rules.maxLength &&
          rules.pattern.test(nationalNumber)) {
        return {
          valid: true,
          country,
          formatted: rules.code + ' ' + nationalNumber
        }
      }
    }
    
    return { valid: false, country: 'unknown', formatted: number }
  }
}

Conclusion

International phone validation requires understanding E.164 standard, implementing country-specific rules, handling diverse formatting conventions, and providing appropriate user feedback. Success depends on maintaining comprehensive country rules, supporting multiple input formats, and providing clear formatting guidance.

Use the Cleariflow Phone Validation API for structural checks and E.164 normalization across 240+ regions — with an optional country hint for national-format input.