Monaco Country Code +377: Phone Number Format & Validation Guide

Monaco's country code is +377. All Monaco phone numbers use this country code and follow the ITU-T E.164 international standard. This comprehensive guide covers how to call Monaco, phone number formats, validation patterns, and telecommunications infrastructure for integrating Monaco phone numbers into your applications.

Quick Reference

• Country: Monaco (Principality of Monaco)
• Country Code: +377 (assigned by ITU-T E.164)
• International Prefix: 00
• National Prefix: None (dial 8-digit numbers directly)
• Emergency Numbers: Police (17), Fire/Ambulance (18), European Emergency (112)
• Primary Telecom Provider: Monaco Telecom
• Timezone: CET (UTC+1), CEST (UTC+2) during daylight saving time

Monaco Phone Number Format and Structure

Monaco phone numbers adhere to the ITU-T E.164 international numbering standard (version 11/2010), ensuring compatibility with global networks, international call routing, number portability, and unified number formatting.

How to Format Monaco Phone Numbers

Monaco phone numbers consist of 8 digits after the +377 country code (e.g., +37792012345). Always store and transmit numbers using the full international E.164 format to avoid ambiguity and ensure compatibility across systems.

Calling within Monaco (domestic dialing): Dial the 8-digit number directly without a prefix.

Calling Monaco internationally: Dial your country's international prefix (00 or +), then 377 (Monaco's country code), then the 8-digit phone number.

Common Formatting Mistakes

Watch for these common errors when processing Monaco phone numbers:

• Including country code in domestic context: Users entering "+377 92012345" when only "92012345" is expected domestically
• Missing leading digits: Entering "2012345" (7 digits) instead of required 8 digits
• Mixing formats: Combining national and international formats like "377 92012345" without the plus sign
• Extra spaces or characters: Input like "+377 (92) 01-23-45" requires sanitization
• Wrong country code: Entering "+33 7" (French mobile prefix) instead of "+377"

Handle these errors with this approach:

1. Strip all non-numeric characters except the leading plus sign
2. Detect and normalize country code (377 or +377)
3. Verify exactly 8 digits remain after country code
4. Store in canonical E.164 format (+377XXXXXXXX)
5. Format for display based on user locale preferences

Monaco Number Types: Mobile, Landline, and Toll-Free

Monaco categorizes phone numbers by their first digit after the country code. The ITU Monaco numbering plan defines these categories:

• Geographic (Landline): +3779XXXXXXX (e.g., +37792012345). Numbers starting with 9 serve fixed-line services across Monte Carlo, La Condamine, Fontvieille, and other districts. Includes special range +377870XXXXX for fixed telecommunications.
• Mobile: Multiple prefixes support mobile services:
  • +3776XXXXXXX (standard 8-digit mobile, e.g., +37761234567)
  • +3773XXXXXXX, +37744XXXXXX through +37746XXXXXX (additional mobile ranges)
  • +3772XXXXXXXXXXXX (12-digit numbers reserved for Machine-to-Machine/IoT services)
• Toll-Free: +377800XXXX (e.g., +3778001234). Free for callers within Monaco, used for business and customer service.
• Special Services: Emergency numbers (17, 18, 112, 141 for duty doctor/pharmacy information) are national-only and cannot be dialed in E.164 format.

Note on premium rate services: Monaco's official numbering plan does not allocate specific premium-rate prefixes. Premium services use standard rate numbers with service-level billing arrangements.

Note: Monaco Telecom manages Monaco's numbering plan. Consult their official documentation for current prefix allocations.

Monaco Phone Number Validation

Validate Monaco phone numbers efficiently using regular expressions (regex) that check for the +377 country code and proper 8-digit formatting.

Input Sanitization and Security Considerations

Implement input sanitization before validation to prevent security vulnerabilities:

function sanitizePhoneInput(input) {
  // Security: Prevent injection attacks
  if (input === null || input === undefined) {
    throw new Error('Phone number input cannot be null or undefined');
  }

  // Convert to string and limit length to prevent DoS
  const str = String(input).slice(0, 20);

  // Remove all characters except digits, +, and common separators
  // This prevents SQL injection, XSS, and command injection
  const sanitized = str.replace(/[^\d+\s\-()]/g, '');

  // Additional validation: reject suspicious patterns
  if (sanitized.includes('--') || sanitized.includes(';;')) {
    throw new Error('Invalid phone number format');
  }

  return sanitized;
}

Security best practices:

• Always sanitize user input before processing
• Use parameterized queries and prepared statements to prevent SQL injection
• Reject inputs exceeding 20 characters
• Allow only digits, plus sign, and standard separators
• Implement rate limiting to prevent endpoint abuse
• Log validation failures to monitor attack patterns

// Enhanced Regular Expressions for Validation
const geoPattern = /^(9|870)\d{5,7}$/;        // Geographic Numbers (9XXXXXXX or 870XXXXX)
const mobilePattern = /^(6|3|4[4-6])\d{7}$/;  // Mobile Numbers (6, 3, or 44-46 prefixes)
const m2mPattern = /^2\d{11}$/;               // Machine-to-Machine (12-digit)
const tollFreePattern = /^800\d{4}$/;         // Toll-Free Numbers

function isValidMonacoNumber(number) {
  try {
    // Sanitize input first
    const sanitized = sanitizePhoneInput(number);

    // Remove non-digit characters and normalize country code
    const cleaned = sanitized.replace(/\D/g, '').replace(/^377/, '');

    // Handle edge cases
    if (!cleaned || cleaned.length === 0) {
      return false;
    }

    // Validate against Monaco patterns
    return (
      geoPattern.test(cleaned) ||
      mobilePattern.test(cleaned) ||
      m2mPattern.test(cleaned) ||
      tollFreePattern.test(cleaned)
    );
  } catch (error) {
    console.error('Validation error:', error.message);
    return false;
  }
}

// Example usage with error handling:
console.log(isValidMonacoNumber('+37792012345')); // true (geographic)
console.log(isValidMonacoNumber('+37761234567')); // true (mobile)
console.log(isValidMonacoNumber('+3778001234'));  // true (toll-free)
console.log(isValidMonacoNumber('+37744123456')); // true (mobile 44 prefix)
console.log(isValidMonacoNumber('+15551234567')); // false (not Monaco)
console.log(isValidMonacoNumber(null));           // false (null input)
console.log(isValidMonacoNumber(''));             // false (empty input)

Phone Number Validation Libraries Comparison

Consider these validation options for production applications:

Recommendation: Use libphonenumber-js for client-side validation and Twilio Lookup API for server-side verification when you need carrier information.

Best Practices for Developers

• Store Numbers in E.164 Format: Always use the international E.164 format (+377XXXXXXXX) to simplify processing and ensure system compatibility.
• Guide User Input: Provide clear instructions and use input masking to help users enter numbers correctly. Implement client-side formatting to improve the user experience.
• Validate on Both Sides: Implement client-side and server-side validation to prevent invalid data from entering your system.
• Handle Errors Clearly: Provide specific, actionable error messages for invalid input. Log validation failures for debugging and monitoring.
• Account for Number Portability: Monaco supports number portability. The number format stays the same, but the carrier may change. Use a service like Twilio Lookup API to identify the current carrier.

Database Schema Recommendations

Store phone numbers in databases with this schema:

-- Recommended schema for phone numbers
CREATE TABLE contacts (
  id SERIAL PRIMARY KEY,
  phone_e164 VARCHAR(15) NOT NULL,  -- E.164 format: +377XXXXXXXX
  phone_country_code VARCHAR(4) DEFAULT '377',
  phone_national VARCHAR(12),  -- National format without country code
  phone_type VARCHAR(20),  -- 'mobile', 'landline', 'tollfree', 'm2m'
  carrier VARCHAR(100),  -- Carrier name (if known)
  is_verified BOOLEAN DEFAULT FALSE,
  verified_at TIMESTAMP,
  created_at TIMESTAMP DEFAULT NOW(),
  updated_at TIMESTAMP DEFAULT NOW(),
  CONSTRAINT phone_e164_format CHECK (phone_e164 ~ '^\+377\d{8,12}$')
);

-- Index for fast lookups
CREATE INDEX idx_phone_e164 ON contacts(phone_e164);
CREATE INDEX idx_phone_type ON contacts(phone_type);

Storage best practices:

• Store in E.164 format as canonical representation
• Add separate column for display formatting preferences
• Index the E.164 column for fast lookups
• Consider storing country code separately for multi-country applications
• Use VARCHAR(15) to accommodate E.164 standard (max 15 digits including +)
• Add CHECK constraints to enforce format at database level

Performance Optimization for Bulk Validation

Validate large batches of phone numbers with this approach:

// Batch validation with caching
class MonacoPhoneValidator {
  constructor() {
    this.cache = new Map();
    this.batchSize = 1000;
  }

  // Validate single number with caching
  validate(number) {
    if (this.cache.has(number)) {
      return this.cache.get(number);
    }

    const result = isValidMonacoNumber(number);
    this.cache.set(number, result);

    // Limit cache size to prevent memory issues
    if (this.cache.size > 10000) {
      const firstKey = this.cache.keys().next().value;
      this.cache.delete(firstKey);
    }

    return result;
  }

  // Bulk validation
  validateBatch(numbers) {
    return numbers.map(num => ({
      number: num,
      valid: this.validate(num)
    }));
  }
}

// Usage
const validator = new MonacoPhoneValidator();
const results = validator.validateBatch([
  '+37792012345',
  '+37761234567',
  '+3778001234'
]);

Performance tips:

• Use caching for repeated validations
• Process in batches to optimize database queries
• Implement async validation for large datasets
• Consider using worker threads for CPU-intensive validation
• Pre-compile regex patterns (done automatically in most engines)

Monaco Telecom: 5G Network and Infrastructure

Monaco Telecom provides Monaco's telecommunications infrastructure, including 5G coverage and high-speed fiber internet services.

5G Network Coverage in Monaco

Monaco Telecom has deployed 5G network coverage throughout Monaco's 2 km² area, serving both residential and business customers.

Technical specifications:

• 5G Band: n78 (3500 MHz) operating in the 3300–3800 MHz range (source)
• Technology: 5G NR with Time Division Duplex (TDD)
• Speed: Up to 10x faster than 4G (theoretical speeds up to 1 Gbps for 5G, compared to 4G's typical 100–300 Mbps)
• Latency: Up to 50x lower latency than 4G (5G: ~1–10ms, 4G: ~30–50ms)
• Coverage: Complete principality coverage across all districts

Key features:

• Wide Coverage: 5G service available across the principality
• Modern Devices: Support for 5G-enabled devices
• High-Speed Data: Enhanced mobile broadband capabilities with speeds up to 1 Gbps
• Low Latency: Ideal for real-time applications like video conferencing and IoT

Monaco Landline and Fiber Internet Services

Monaco Telecom offers fiber-optic internet and traditional landline services:

• Fiber Internet: Speeds up to 10 Gbps for dedicated fiber (FTTO – Fiber to the Office) for businesses; consumer fiber (FTTH) typically up to 1 Gbps with Wi-Fi 6 support
• Dedicated Fiber (FTTO): Symmetrical guaranteed bandwidth, low latency, customizable and scalable, with 2–4 hour guaranteed restoration time
• Fixed-Line Telephony: Landline services using the +3779XXXXXXX and +377870XXXXX number ranges
• Business Services: Enterprise connectivity solutions including TrunkSIP, Voice 365, hosting, and cloud services

How Number Portability Works in Monaco

Monaco supports number portability, allowing you to switch providers while keeping your phone number. Based on European number portability standards, the process includes:

Process overview:

• Validation Phase: Initial request verification and eligibility check with current provider
• Processing Phase: Transfer coordination between operators; technical setup and testing
• Completion Phase: Number activation with new provider; old service deactivation

Timeframes and requirements:

• Standard porting time: 5–10 business days
• Express porting: Available for additional fees; contact Monaco Telecom for details
• Required documentation:
  • Valid photo ID (passport or Monaco residence card)
  • Current account details with existing provider
  • Number portability authorization code (PAC) from current provider
  • Proof of address in Monaco
  • Business registration documents (for business numbers)
• Porting fees: €0–€20 for mobile, €0–€50 for business lines (varies by provider)
• Restrictions: Numbers must be active, in good standing (no outstanding bills), and past minimum contract period

Common issues and troubleshooting:

• Porting rejection: Verify account information matches provider records exactly
• Delayed porting: Contact both old and new providers; may occur during high-traffic periods
• Service interruption: Brief downtime (<1 hour) during cutover; plan accordingly
• Failed activation: Check device compatibility and APN settings for mobile numbers

Contact Monaco Telecom at +377 99 66 33 00 for current portability procedures, exact timeframes, and fee schedules.

Frequently Asked Questions

What is Monaco's country code?

Monaco's country code is +377. To call Monaco from abroad, dial your country's international exit code (typically 00 or 011), followed by 377, then the 8-digit Monaco phone number. For example, from the US dial: 011-377-92-01-23-45.

How do I call a Monaco number?

To call Monaco from overseas, dial your international access code + 377 + 8-digit number. Within Monaco, dial the 8-digit number directly. Store Monaco numbers in international E.164 format: +377 followed by 8 digits (e.g., +37792012345).

What are Monaco mobile phone number prefixes?

Monaco mobile numbers typically start with 6 (e.g., +3776XXXXXXX) and are supported on Monaco Telecom's 4G/5G network. Additional mobile prefixes include 3, 44, 45, and 46. All mobile numbers are 8 digits after the +377 country code.

What are Monaco emergency numbers?

Monaco emergency numbers are: Police (17), Fire/Ambulance (18), and European Emergency (112). These numbers work from any phone in Monaco.

Does Monaco have toll-free numbers?

Yes. Monaco toll-free numbers start with 800 (e.g., +377800XXXX) and are free for callers within Monaco. Businesses commonly use these for customer service.

How do I call Monaco from the United States?

From the US, dial 011 (US international prefix), then 377 (Monaco country code), then the 8-digit Monaco number. Example: 011-377-92-01-23-45.

How do I call Monaco from the United Kingdom?

From the UK, dial 00 (UK international prefix), then 377 (Monaco country code), then the 8-digit number. Example: 00-377-92-01-23-45.

Can I send SMS messages to Monaco numbers?

Yes. Monaco mobile numbers (starting with 6, 3, or 44–46) fully support SMS and MMS messaging. International SMS delivery depends on your carrier's roaming agreements with Monaco Telecom. Standard international SMS rates apply when texting Monaco from abroad.

Do Monaco phone numbers work with WhatsApp?

Yes. Monaco mobile numbers work with WhatsApp, Signal, Telegram, and other messaging apps that use phone number verification. Monaco Telecom provides full 4G/5G data services for app-based messaging.

Additional Considerations

Regulatory Framework

Monaco maintains telecommunications regulations governing service providers and infrastructure, with data protection laws aligned with European standards.

Data Protection and Privacy Compliance:

Monaco updated its data protection legislation with Law No. 1.565 of December 3, 2024, offering GDPR-equivalent protections:

• Registration Required: Register with the Commission de Contrôle des Informations Nominatives (CCIN) before processing personal data (including phone numbers)
• Legal Basis Required: Process phone numbers only with consent, contractual necessity, legal obligation, public interest, or legitimate interest
• Data Subject Rights: Individuals have rights to access, rectification, and opposition to data processing
• Cross-border Transfers: Transfers to non-adequate countries require CCIN authorization; EU transfers benefit from adequacy arrangements
• No Mandatory Breach Notification: Unlike GDPR, Monaco law does not require breach notification, but best practices recommend it
• Penalties: €9,000–€90,000 fines and/or 1 month–1 year imprisonment for violations

Marketing and Consent Requirements:

• Electronic Marketing: Notify CCIN before implementing marketing activities using phone numbers
• Consent Standard: Obtain explicit consent before marketing communications; pre-checked boxes are insufficient
• Opt-out Rights: Provide clear mechanisms for users to oppose marketing use
• Record Keeping: Maintain documentation of consent and processing activities

Business Number Registration:

For businesses acquiring Monaco phone numbers:

• Register business entity with Monaco authorities
• Provide proof of Monaco business address or operations
• Complete Monaco Telecom service application with business documentation
• Comply with CCIN registration if processing customer phone data

Compliance contacts:

• Service-Specific Requirements: Monaco Telecom
• Data Protection Authority: CCIN (Commission de Contrôle des Informations Nominatives)
• Regulatory and Licensing Information: Direction du Développement des Usages Numériques at +377 98 98 88 00

Service Contact Information

Monaco Telecom Customer Service:

• Phone: +377 99 66 33 00
• Business Phone: +377 99 66 68 86
• Email: service.client@monaco-telecom.mc
• Business Email: contact-entreprises@monaco-telecom.mc
• Hours: Monday–Saturday, 8:00–22:00 (personal); Monday–Saturday 9:00–19:00 (business)
• WhatsApp Support: +377 377 10 000
• Website: www.monaco-telecom.mc

Store Locations:

• Fontvieille: 9 Rue du Gabian, 98000 Monaco (Mon–Fri 9am–6pm, Sat 9am–5:30pm)
• Monte-Carlo: 27 Bd des Moulins, 98000 Monaco (Mon–Fri 10am–1pm/2pm–7pm)

Development Best Practices

Build applications for Monaco's market:

• Store all phone numbers in E.164 format (+377XXXXXXXX)
• Implement validation using the patterns in this guide
• Account for number portability in carrier identification logic
• Test with Monaco Telecom's network characteristics
• Stay updated on Monaco Telecom's technical documentation

Testing Strategies and QA Checklist

Test data examples for Monaco numbers:

// Valid test numbers (use only in test environments)
const testNumbers = {
  geographic: ['+37792000001', '+37793000001', '+37799999999'],
  mobile: ['+37760000001', '+37761000001', '+37769999999'],
  mobile_alt: ['+37730000001', '+37744000001', '+37746999999'],
  tollfree: ['+3778000001', '+3778009999'],
  m2m: ['+377200000000001', '+377299999999999'],
  invalid: [
    '+37712345678',  // wrong prefix
    '+3779201234',   // too short
    '+377920123456', // too long
    '+337920123456', // wrong country code
    '920123456'      // missing country code
  ]
};

QA checklist:

• Validates all legitimate Monaco number formats (9, 6, 3, 44–46, 800, 2, 870)
• Rejects invalid country codes and malformed inputs
• Handles null, undefined, and empty string inputs gracefully
• Sanitizes input to prevent injection attacks
• Correctly converts between national and international formats
• Stores in E.164 format in database
• Displays formatted numbers according to user locale
• Implements rate limiting on validation endpoints
• Logs validation failures for monitoring
• Handles number portability (carrier may differ from prefix)
• Tests with real Monaco Telecom network (if applicable)
• Validates SMS/MMS delivery to Monaco numbers
• Checks international dialing from multiple countries
• Verifies error messages are clear and actionable

API Rate Limiting and Error Handling

// Rate limiting example for validation endpoint
const rateLimit = require('express-rate-limit');

const validationLimiter = rateLimit({
  windowMs: 15 * 60 * 1000, // 15 minutes
  max: 100, // limit each IP to 100 requests per windowMs
  message: {
    error: 'Too many validation requests',
    retryAfter: '15 minutes'
  },
  standardHeaders: true,
  legacyHeaders: false,
});

// Error handling with specific error codes
app.post('/api/validate-phone', validationLimiter, (req, res) => {
  try {
    const { phoneNumber } = req.body;

    if (!phoneNumber) {
      return res.status(400).json({
        error: 'MISSING_PHONE_NUMBER',
        message: 'Phone number is required'
      });
    }

    const isValid = isValidMonacoNumber(phoneNumber);

    if (!isValid) {
      return res.status(422).json({
        error: 'INVALID_PHONE_NUMBER',
        message: 'Phone number format is invalid for Monaco',
        expected: '+377 followed by 8 digits (e.g., +37792012345)'
      });
    }

    res.json({
      valid: true,
      e164: formatToE164(phoneNumber),
      type: detectNumberType(phoneNumber)
    });

  } catch (error) {
    console.error('Validation error:', error);
    res.status(500).json({
      error: 'VALIDATION_ERROR',
      message: 'An error occurred during validation'
    });
  }
});

Error codes to implement:

• MISSING_PHONE_NUMBER: Required field not provided
• INVALID_FORMAT: Does not match Monaco number patterns
• INVALID_COUNTRY_CODE: Wrong country code provided
• INVALID_LENGTH: Too short or too long
• RATE_LIMIT_EXCEEDED: Too many requests
• VALIDATION_ERROR: General validation failure

Common Integration Issues and Troubleshooting

Issue: Numbers validated but SMS not delivered

• Cause: Mobile number inactive, out of service area, or carrier filtering
• Solution: Use Twilio Lookup or similar service to verify number is active and reachable; check carrier status

Issue: Validation passes but phone calls fail

• Cause: Number portability changed carrier, number disconnected, or VoIP compatibility issues
• Solution: Perform real-time carrier lookup; verify number is still active; check SIP/VoIP trunk configuration

Issue: International calls to Monaco fail

• Cause: Incorrect dialing format, carrier blocking, or routing issues
• Solution: Verify international prefix for originating country (00 or 011); ensure complete format: prefix + 377 + 8 digits

Issue: Database storing incorrectly

• Cause: Character encoding issues, field length too short, or format inconsistencies
• Solution: Use VARCHAR(15) minimum for E.164; store with + symbol; implement CHECK constraint; use UTF-8 encoding

Issue: High validation latency

• Cause: Complex regex, lack of caching, or API dependency
• Solution: Implement caching layer; pre-compile regex patterns; use async validation; consider local validation library

Issue: GDPR/compliance violations

• Cause: Processing phone numbers without legal basis or CCIN registration
• Solution: Register with CCIN; obtain explicit consent; document legal basis; implement data subject rights

Issue: Different carriers for same prefix

• Cause: Number portability allows users to keep numbers when switching carriers
• Solution: Do not assume carrier from prefix; use Twilio Lookup or carrier detection API for current carrier

Build robust applications that integrate seamlessly with Monaco's telecommunications infrastructure. Verify current technical specifications with Monaco Telecom for production deployments.