Validating phone numbers correctly is a complex task, especially when an application serves users from multiple countries. Each country has its own numbering plan, with differences in number lengths, formats, prefixes, and special codes. To provide a smooth user experience and ensure data accuracy, developers must implement country-specific phone number validations. Here’s how this is typically done.
1. Understanding Country Numbering Plans
Each country’s telephone numbering plan is governed by international and national regulations, often following the ITU-T E.164 standard as a framework. Key differences include:
Country Code: Each country has a unique dialing prefix (e.g., +1 for the US, +91 for India).
Number Length: The total length of the phone number (including country code) varies.
Local Formats: The grouping of digits, use of area codes, and presence of trunk prefixes differ.
Special Numbers: Emergency numbers, toll-free numbers, and premium-rate numbers have distinct patterns.
2. Using Libraries for Validation
To handle this complexity, developers rarely build recent mobile phone number data validations from scratch. Instead, they use well-maintained libraries like Google’s libphonenumber, which:
Contains detailed metadata for almost all countries’ numbering plans.
Provides functions to parse, validate, format, and normalize phone numbers.
Automatically detects invalid numbers based on country-specific rules.
Supports checking number types (mobile, landline, toll-free, etc.) by country.
By integrating such libraries, apps can validate numbers accurately regardless of the user's country.
3. Country Selection and Input UI
Country-specific validation often starts with the user interface design:
Country Dropdown: Users select their country before entering their number, enabling the app to apply the correct validation rules.
Automatic Country Detection: Using IP geolocation or device locale, apps can pre-fill the country code or adjust the validation dynamically.
Input Masking: The input field can display a mask that guides users to enter numbers in the correct format for their country.
This approach helps users input valid numbers and reduces errors.
4. Validation Workflow
When a user enters a phone number:
Normalize Input: Remove spaces, dashes, and other formatting characters.
Detect Country Code: Extract or infer the country code from the input or user selection.
Apply Country Rules: Check the remaining number against the country’s length and format rules.
Use Library Functions: Call validation functions from libphonenumber or similar tools to confirm validity.
Provide Feedback: Prompt users with real-time validation errors or formatting corrections.
5. Handling Edge Cases
Country-specific validations must also consider:
Number Portability: Users may keep their numbers when switching carriers or regions within a country.
International Numbers: Users may enter numbers from countries other than their own, so apps should allow and validate international formats.
Temporary or Virtual Numbers: Some countries have specific prefixes or ranges for VoIP or temporary numbers, which may be handled differently.
6. Testing and Updates
Phone numbering plans can change, so apps need:
Regular Updates: Update libraries and data to keep up with new country codes or numbering changes.