How do you validate mobile numbers?

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Validating mobile numbers is a crucial step in many applications, from user registration and contact forms to marketing campaigns and security features like two-factor authentication. It ensures that the number provided is not only syntactically correct but also potentially active and reachable. The process of validation can involve several layers, each increasing the accuracy and reliability of the number.

The most basic level of mobile number validation involves syntactic validation, which checks if the number conforms to a generally accepted format. This is often done using regular expressions (regex). For example, a simple regex might check for a specific number of digits, allow for optional country codes (e.g., "+1" for the US, "+880" for Bangladesh), and permit various separators like spaces, hyphens, or tunisia mobile database parentheses. However, this level of validation is limited. A number like "555-123-4567" might pass a regex for a US format, but it doesn't guarantee that it's a real, active phone number. International numbers add significant complexity due to varying lengths, country codes, and national dialing plan nuances. Many countries have unique rules regarding the starting digits, total length, and internal structure of their phone numbers.

A more robust approach involves country-specific validation, which takes into account the numbering plan of a particular country. This is where libraries like Google's libphonenumber become invaluable. These libraries contain comprehensive data on the valid phone number formats for virtually every country in the world, including minimum and maximum lengths, valid prefixes, and specific patterns for mobile versus landline numbers. By using such a library, you can not only determine if a number is valid for a given country but also parse it into a standardized E.164 format (e.g., which is globally unique and essential for international communication. This level of validation significantly reduces the chances of accepting invalid or malformed numbers.

The highest level of validation is real-time verification, which involves actively checking if a mobile number is live and capable of receiving calls or SMS messages. This is typically done through third-party APIs offered by communication service providers (like Twilio, Vonage, or specialized phone validation services). These APIs can perform "lookups" that go beyond format checking to provide information such as:

Line type: Whether it's a mobile, landline, or VoIP number. This is crucial for determining the appropriate communication method (e.g., SMS for mobile, voice for landline).
Carrier information: The mobile network operator (e.g., Grameenphone, Robi, Airtel in Bangladesh).
Active status: Whether the number is currently in service or disconnected.
Roaming status: If the user is currently roaming in a different country.
Fraud risk scores: Some services can even assess the likelihood of a number being associated with fraudulent activity. This real-time verification often involves a small cost per lookup but provides the highest confidence in the validity and reachability of a mobile number, which is particularly important for critical applications like account recovery or transaction confirmations.