E164 Format: Specifications and Phone Number Validation Guide

E.164 Format: Specifications and Phone Number Validation Guide

Understanding E.164: The Global Phone Number Standard

The E.164 standard represents the backbone of international telecommunications, providing a unified framework for phone number formatting across all public networks worldwide. Established by the International Telecommunication Union (ITU), this standard ensures consistent communication routing and interoperability between different countries and network operators.

Historical Context and Evolution

Originally introduced in 1984, the E.164 standard has evolved to accommodate the growing complexity of global telecommunications. The latest revision (2010) addresses modern requirements including:

  • Mobile number portability
  • IP telephony integration
  • Emergency service requirements
  • International roaming capabilities

Technical Specifications

Number Structure Breakdown

An E.164 number consists of three essential components, working together to ensure accurate routing:

  1. Country Code (CC)

    • Length: 1-3 digits
    • Examples: +1 (North America), +44 (UK), +86 (China)
    • Assigned by ITU-T

  2. National Destination Code (NDC)

    • Variable length (typically 2-4 digits)
    • Identifies geographic areas or services
    • Managed by national authorities

  3. Subscriber Number (SN)

    • Remaining digits (up to total 15 digits)
    • Unique identifier within the NDC zone
Example Breakdown:
+1 (415) 555-0123
│  │    └─────── Subscriber Number
│  └──────────── National Destination Code
└─────────────── Country Code

Format Requirements

E.164 numbers must strictly adhere to these specifications:

  1. Character Set

    • Only digits 0-9 allowed
    • Plus (+) prefix permitted for display only
    • No spaces, hyphens, or other separators in stored format

  2. Length Constraints

    • Minimum: CC length + 1 digit
    • Maximum: 15 digits total
    • Country-specific minimum lengths apply

  3. Structural Rules

    // Valid E.164 format regex
const e164Regex = /^\+[1-9]\d{1,14}$/;

Implementation Guide

Validation Strategy

Implement a multi-layer validation approach:

  1. Basic Format Validation

    function isBasicE164Format(number) {
  return /^\+[1-9]\d{1,14}$/.test(number);
}

  2. Country-Specific Validation

    function isValidCountryNumber(number, countryCode) {
  const countryPatterns = {
    '1': /^\+1[2-9]\d{9}$/, // North America
    '44': /^\+44[1-9]\d{9}$/, // UK
    // Add other country patterns
  };
  return countryPatterns[countryCode]?.test(number) || false;
}

  3. Length Validation

    function isValidLength(number, countryCode) {
  const lengths = {
    '1': 11,  // +1 plus 10 digits
    '44': 12, // +44 plus 10 digits
    // Add other country lengths
  };
  return number.length === lengths[countryCode];
}

Common Edge Cases

Handle these scenarios in your implementation:

  1. International Display Format

    function formatForDisplay(e164Number) {
  // +1-415-555-0123
  return e164Number.replace(/(\+\d{1})(\d{3})(\d{3})(\d{4})/, '$1-$2-$3-$4');
}

  2. Local Format Conversion

    function toE164Format(localNumber, countryCode) {
  // Remove all non-digit characters
  const cleaned = localNumber.replace(/\D/g, '');
  return `+${countryCode}${cleaned}`;
}

Best Practices

  1. Storage

    • Always store in pure E.164 format
    • Remove all formatting characters
    • Include country code validation

  2. Display

    • Use local formatting for user interface
    • Maintain E.164 format in system operations
    • Consider cultural formatting preferences

  3. Validation

    • Implement progressive validation
    • Validate at both input and processing
    • Consider using established libraries for complex validation

Troubleshooting Guide

Common issues and solutions:

  1. Invalid Country Codes

    • Verify against ITU-T assigned codes
    • Check for recent country code changes
    • Validate length against country specifications

  2. Format Inconsistencies

    • Strip all formatting before validation
    • Normalize numbers before comparison
    • Handle international prefix variations

  3. Regional Variations

    • Account for variable NDC lengths
    • Consider mobile number formats
    • Handle special service numbers

Using the Phone Library for E.164 Number Formatting and Validation

The phone npm package provides enterprise-grade E.164 format standardization and validation capabilities for international phone numbers. This production-ready library efficiently handles diverse input formats while ensuring strict compliance with international telecommunication standards according to ITU-T specifications.

Installation and Setup

Get started by installing the package via npm:

npm install phone --save
# or using yarn
yarn add phone

Initialize the library in your project:

const { phone } = require('phone');
// or using ES modules
import { phone } from 'phone';

Comprehensive E.164 Validation

The library implements validation according to the latest ITU-T E.164 specification, enforcing:

  • Maximum length of 15 digits
  • Mandatory '+' prefix followed by country code
  • Strict numerical-only format after the '+' symbol
  • Country-specific number length requirements
  • Valid area code ranges per region

Advanced Validation Features

The library provides sophisticated validation capabilities:

// Basic validation with country detection
const result = phone('+1234567890');
console.log(result.isValid); // Validates number format

// Country-specific validation
const ukResult = phone('+447911123456', { country: 'GB' });
console.log(ukResult.isValid); // Validates UK mobile format

// Landline validation
const landline = phone('+442071234567', { 
  validateMobilePrefix: false,
  country: 'GB' 
});

Error Handling and Validation States

The library provides detailed error feedback for various validation scenarios:

try {
  const result = phone('+invalid');
  if (!result.isValid) {
    console.log('Validation failed:', {
      number: result.phoneNumber,
      country: result.countryIso2,
      error: result.error
    });
  }
} catch (error) {
  console.error('Processing error:', error.message);
}

Performance Optimization

For high-volume validation scenarios, consider these optimization patterns:

// Batch validation
const numbers = ['+1234567890', '+447911123456'];
const results = numbers.map(num => {
  const { isValid, phoneNumber } = phone(num);
  return { original: num, isValid, formatted: phoneNumber };
});

// Cached validation for repeated checks
const validationCache = new Map();
function validateWithCache(number) {
  if (validationCache.has(number)) {
    return validationCache.get(number);
  }
  const result = phone(number);
  validationCache.set(number, result);
  return result;
}

Security Best Practices

Implement these security measures when handling phone numbers:

  1. Sanitize inputs before validation
  2. Store numbers in E.164 format only
  3. Implement rate limiting for validation requests
  4. Log validation attempts for security monitoring
  5. Use secure channels for validation communications

Implementation Examples

Common usage patterns:

// User input validation
function validateUserPhone(input, countryCode) {
  const result = phone(input, { 
    country: countryCode,
    validateMobilePrefix: true,
    strictDetection: true
  });
  
  return {
    isValid: result.isValid,
    formattedNumber: result.phoneNumber,
    countryInfo: {
      iso2: result.countryIso2,
      iso3: result.countryIso3,
      code: result.countryCode
    },
    error: result.error
  };
}

// Database storage preparation
function preparePhoneForStorage(phoneNumber) {
  const { isValid, phoneNumber: formatted } = phone(phoneNumber);
  if (!isValid) {
    throw new Error('Invalid phone number for storage');
  }
  return formatted; // Returns E.164 formatted number
}

Using libphonenumber-js for Phone Number Validation and Formatting

libphonenumber-js provides a lightweight, modern implementation of Google's phone number handling library, specifically optimized for web applications. This efficient alternative delivers essential phone number validation and formatting capabilities while maintaining a minimal footprint in your application bundle.

Understanding the Implementation Landscape

Before diving into implementation, it's important to understand where libphonenumber-js fits in your technology stack:

  • Bundle Size Optimization: At 145 kB total (65 kB code + 80 kB metadata), it's significantly smaller than Google's original 550 kB implementation
  • Modern JavaScript Support: Built with ES6+ features and tree-shaking support
  • Framework Compatibility: Seamlessly integrates with React, Vue, and other modern frameworks
  • Browser Performance: Optimized for client-side validation and formatting

Implementation Guide

1. Installation and Basic Setup

Begin by installing the package:

npm install libphonenumber-js --save
# or
yarn add libphonenumber-js

2. Core Validation Implementation

import { parsePhoneNumber, isValidPhoneNumber } from 'libphonenumber-js'

// Basic validation implementation
function validatePhoneNumber(input, countryCode = 'US') {
  try {
    const phoneNumber = parsePhoneNumber(input, countryCode)
    return {
      isValid: phoneNumber.isValid(),
      formatted: phoneNumber.formatInternational(),
      type: phoneNumber.getType(),
      countryCode: phoneNumber.country
    }
  } catch (error) {
    console.error('Phone validation error:', error)
    return { isValid: false, error: error.message }
  }
}

3. Advanced Features Implementation

import { AsYouType, getExampleNumber } from 'libphonenumber-js/max'

// Real-time formatting
const formatter = new AsYouType('US')
inputElement.addEventListener('input', (e) => {
  const formatted = formatter.input(e.target.value)
  e.target.value = formatted
})

// Example number generation for placeholders
const exampleNumber = getExampleNumber('US')
inputElement.placeholder = exampleNumber.formatNational()

Performance Optimization Strategies

Implement these strategies to maintain optimal performance:

  1. Metadata Loading:
// Import minimal metadata for basic validation
import { parsePhoneNumber } from 'libphonenumber-js/min'

// Import full metadata for advanced features
import { parsePhoneNumber } from 'libphonenumber-js/max'
  1. Lazy Loading Pattern:
// Implement lazy loading for advanced features
const loadAdvancedValidation = async () => {
  const { parsePhoneNumber } = await import('libphonenumber-js/max')
  return parsePhoneNumber
}

Error Handling and Validation Patterns

Implement robust error handling:

function validateWithFallback(phoneNumber, country) {
  try {
    const parsed = parsePhoneNumber(phoneNumber, country)
    if (!parsed.isValid()) {
      return {
        isValid: false,
        error: 'Invalid number format',
        suggestions: getNumberSuggestions(phoneNumber, country)
      }
    }
    return {
      isValid: true,
      formatted: parsed.formatInternational(),
      metadata: {
        type: parsed.getType(),
        country: parsed.country
      }
    }
  } catch (error) {
    return handleValidationError(error)
  }
}

function handleValidationError(error) {
  // Implement specific error handling based on error types
  const errorTypes = {
    'INVALID_COUNTRY': 'Unsupported country code',
    'NOT_A_NUMBER': 'Input contains invalid characters',
    'TOO_SHORT': 'Number is too short',
    'TOO_LONG': 'Number exceeds maximum length'
  }
  return {
    isValid: false,
    error: errorTypes[error.code] || 'Validation failed',
    originalError: error
  }
}

Framework Integration Examples

React Integration:

import { useState, useCallback } from 'react'
import { parsePhoneNumber } from 'libphonenumber-js'

const PhoneInput = ({ onValidChange }) => {
  const [value, setValue] = useState('')
  const [isValid, setIsValid] = useState(false)

  const handleChange = useCallback((event) => {
    const input = event.target.value
    setValue(input)
    
    try {
      const phoneNumber = parsePhoneNumber(input, 'US')
      const valid = phoneNumber.isValid()
      setIsValid(valid)
      onValidChange(valid ? phoneNumber.format('E.164') : null)
    } catch (error) {
      setIsValid(false)
      onValidChange(null)
    }
  }, [onValidChange])

  return (
    <div className="phone-input-container">
      <input
        type="tel"
        value={value}
        onChange={handleChange}
        className={`phone-input ${isValid ? 'valid' : 'invalid'}`}
      />
      {!isValid && value && (
        <span className="error-message">Please enter a valid phone number</span>
      )}
    </div>
  )
}

Monitoring and Debugging

Implement logging for validation patterns:

const phoneValidationMetrics = {
  attempts: 0,
  successful: 0,
  failed: 0,
  patterns: new Map()
}

function logValidationAttempt(input, result) {
  phoneValidationMetrics.attempts++
  result.isValid ? 
    phoneValidationMetrics.successful++ : 
    phoneValidationMetrics.failed++
  
  // Track common patterns
  const pattern = input.replace(/\d/g, 'N')
  phoneValidationMetrics.patterns.set(
    pattern,
    (phoneValidationMetrics.patterns.get(pattern) || 0) + 1
  )
}

Using the google-libphonenumber Library for Phone Number Parsing and Validation

The google-libphonenumber library provides enterprise-grade phone number validation and formatting capabilities for Node.js applications. This official Node.js implementation of Google's phone number handling system enables robust international phone number processing with comprehensive parsing, formatting, and validation features.

Installation and Basic Setup

Install via npm:

npm install --save-prod google-libphonenumber

Initialize the core components:

const PhoneNumberUtil = require('google-libphonenumber').PhoneNumberUtil;
const PNF = require('google-libphonenumber').PhoneNumberFormat;
const phoneUtil = PhoneNumberUtil.getInstance();

Core Features and Implementation

1. Basic Phone Number Parsing

// Parse with region code
const parseNumber = (rawNumber, defaultCountry = 'US') => {
  try {
    return phoneUtil.parse(rawNumber, defaultCountry);
  } catch (err) {
    console.error('Parsing error:', err.message);
    return null;
  }
};

// Example usage
const number = parseNumber('(415) 555-0123', 'US');
console.log(phoneUtil.format(number, PNF.INTERNATIONAL));
// Output: +1 415 555 0123

2. Comprehensive Validation

const validatePhoneNumber = (number, region) => {
  try {
    const parsedNumber = phoneUtil.parse(number, region);
    return {
      isValid: phoneUtil.isValidNumber(parsedNumber),
      isPossible: phoneUtil.isPossibleNumber(parsedNumber),
      type: phoneUtil.getNumberType(parsedNumber),
      region: phoneUtil.getRegionCodeForNumber(parsedNumber)
    };
  } catch (err) {
    return {
      isValid: false,
      error: err.message
    };
  }
};

3. Formatting Options

const formatPhoneNumber = (parsedNumber) => ({
  e164: phoneUtil.format(parsedNumber, PNF.E164),
  international: phoneUtil.format(parsedNumber, PNF.INTERNATIONAL),
  national: phoneUtil.format(parsedNumber, PNF.NATIONAL),
  rfc3966: phoneUtil.format(parsedNumber, PNF.RFC3966)
});

Performance and Size Comparison

When compared to alternative libraries source:

  • Bundle Size
    • google-libphonenumber: ~550 KB (350 KB code + 200 KB metadata)
    • libphonenumber-js: ~145 KB (65 KB code + 80 KB metadata)

The larger size of google-libphonenumber is offset by its comprehensive validation capabilities and complete metadata coverage.

Version Compatibility

The library maintains compatibility with Node.js versions through its zero-dependency architecture source. Key compatibility points:

  • Supports Node.js 12.x and above
  • Regular metadata updates to maintain carrier and region accuracy
  • Backwards compatible API through major versions

E.164 Compliance and Validation

The library implements the latest ITU-T E.164 specifications source:

// E.164 validation example
const number = phoneUtil.parse('12133734253', 'US');
const isValidE164 = phoneUtil.isValidNumber(number) && 
                    number.getCountryCode() &&
                    number.getNationalNumber().length <= 12;

Key validation rules include:

  • Country code: 1-3 digits
  • Subscriber number: Maximum 12 digits
  • Total length: Maximum 15 digits

Error Handling Best Practices

Implement robust error handling for parsing failures:

try {
  const number = phoneUtil.parse(rawNumber, defaultCountry);
  if (!phoneUtil.isValidNumber(number)) {
    throw new Error('Invalid number format');
  }
  return number;
} catch (err) {
  if (err instanceof Error) {
    console.error('Parsing error:', err.message);
    // Handle specific error cases
  }
  throw err;
}

Testing and Validation

For comprehensive testing, implement validation across multiple number formats:

// Test suite example
const testNumber = phoneUtil.parse('202-456-1414', 'US');

// Format validation
assert(phoneUtil.format(testNumber, PNF.E164) === '+12024561414');

// Regional validation
assert(phoneUtil.isValidNumberForRegion(testNumber, 'US') === true);

// Type checking
assert(phoneUtil.getNumberType(testNumber) === 
       PhoneNumberType.FIXED_LINE_OR_MOBILE);

Browser Compatibility and Implementation Guide

The intl-tel-input library provides comprehensive cross-browser support while maintaining optimal performance and accessibility standards. This guide covers compatibility details, implementation best practices, and optimization strategies.

Core Browser Support Matrix

BrowserMinimum VersionSupport LevelNotable Features
ChromeLatest✓ FullAll features, optimal performance
FirefoxLatest✓ FullComplete functionality, including custom dropdowns
Safari14+✓ FullFull mobile support, touch optimization
EdgeLatest✓ FullNative Windows integration

Mobile Implementation

The library automatically optimizes for mobile devices through several key features:

  1. Responsive Interface

    • Fullscreen country selection popup for better mobile UX
    • Touch-optimized dropdown controls
    • Automatic input type switching for mobile keyboards

  2. Performance Optimization

    const iti = window.intlTelInput(input, {
  utilsScript: "path/to/utils.js",
  initialCountry: "auto",
  separateDialCode: true,
  useFullscreenPopup: true  // Optimized for mobile
});

Resource Loading Strategy

The library implements efficient resource management:

  1. Utils Script Loading

    • Asynchronous loading of utils.js (260KB)
    • Automatic lazy loading after page content
    • Support for modern bundler optimizations:
    // Webpack example
import 'intl-tel-input/build/js/utils';

  2. Bundle Optimization

    // Modern bundler configuration
{
  optimization: {
    splitChunks: {
      chunks: 'async',
      name: 'intl-tel-input-utils'
    }
  }
}

Accessibility Implementation

The library provides comprehensive accessibility support:

  1. ARIA Integration

    const input = document.querySelector("#phone");
window.intlTelInput(input, {
  customContainer: "iti-container-id",
  ariaLabel: "Phone number",
  customPlaceholder: function(selectedCountryPlaceholder) {
    return `Enter ${selectedCountryPlaceholder}`;
  }
});

  2. Keyboard Navigation

    • Full keyboard support for country selection
    • Focus management for modal dialogs
    • Screen reader announcements for status changes

Implementation Best Practices

  1. Version Management

    // Package.json
{
  "dependencies": {
    "intl-tel-input": "^24.6.0"  // Use semantic versioning
  }
}

  2. Error Handling

    iti.promise.then(() => {
  // Utils script loaded successfully
}).catch(err => {
  console.error('Utils script loading failed:', err);
  // Implement fallback behavior
});

  3. Testing Recommendations

    • Cross-browser testing on target platforms
    • Mobile device testing with various screen sizes
    • Accessibility audit using screen readers
    • Performance monitoring with browser dev tools

For optimal implementation, ensure proper error handling and progressive enhancement strategies are in place, especially for environments where certain features may not be fully supported.