What Is Google’s libphonenumber?
libphonenumber is Google’s open-source toolkit for handling international phone numbers. It enables:
- Parsing raw input
- Formatting into national and international styles
- Performing pattern-based checks
It supports Java, C++, and JavaScript, and powers formatting logic in many products you already use.
Why Developers Choose It 🧑💻
✔️ Trustworthy (maintained by Google)
- Fast updates, accurate metadata, and strong community adoption.
✔️ Handles global complexity
- The library knows the rules for nearly every country: digit lengths, area codes, prefixes, carrier blocks, and more.
✔️ Completely free and open-source
- Ideal for front-end formatting and preliminary validation.
Using libphonenumber-js (The JavaScript Port)
Most web and Node developers use libphonenumber-js, a lightweight and ergonomic port of the original library.
This guide will use it for all code examples.
How to Perform Syntactical Validation with libphonenumber-js 🧪
This section explains how to use the library correctly—and what each method actually does.
Step 1: Install the Library 📦
npm install libphonenumber-js
Step 2: Parse User Input
Parsing transforms a raw string into a structured PhoneNumber object.
import { parsePhoneNumber } from 'libphonenumber-js';
const rawNumber = '(213) 373-4253';
const defaultCountry = 'US';
try {
const phoneNumber = parsePhoneNumber(rawNumber, defaultCountry);
} catch (error) {
console.error('Error parsing phone number:', error.message);
}
The default country helps interpret non-international inputs.
Step 3: Understanding Validation Functions (The Confusing Part) 🤯
This is where confusion happens. Developers often assume:
- “If is Valid() returns true, the number is good to go.”
But that’s not true. These functions do not confirm if the number exists.
The Quick Check: isPossible() ⚡
This is a minimal, length-based check:
✔️ Checks if the number has enough digits
✔️ Checks if it isn’t too long
❌ Does not check prefixes or area codes
- if (phoneNumber && phoneNumber.isPossible()) {
// The number length is plausible
}
The Full Pattern Check: isValid() 🧠
This checks the number against complex, country-specific rules.
- if (phoneNumber && phoneNumber.isValid()) {
console.log('This number format is valid!');
} else {
console.log('This number format is NOT valid.');
}
A Clear Explanation:
- isPossible() = “The length seems ok.”
- isValid() = “The format matches the numbering rules for that country.”
- Neither = “This number is real or active.”
Bonus: As-You-Type Formatter for Better UX ✨
- import { AsYouType } from 'libphonenumber-js';
const formatter = new AsYouType('US');
console.log(formatter.input('2133734'));
Useful for improving forms and reducing user mistakes.
The Critical Limitation: Syntactical vs. Real-Time Validation ⚠️
Even if a number passes all libphonenumber checks, it may still be:
- Deactivated
- Unassigned
- A VoIP or disposable number
- Incorrectly formatted but still considered valid
This happens because libphonenumber relies on:
Static Metadata
- It contains a huge database of numbering rules, but no live telecom data.
What libphonenumber Cannot Tell You ❌
❌ Is the number real?
+18005550199 is perfectly valid syntactically — yet it’s a reserved demo number.
❌ Is the number active?
A disconnected mobile number still passes isValid().
❌ What’s the true line type?
VoIP numbers often share the same structure as mobile numbers.
All of these create major issues for signup flows, 2FA, fraud prevention, and SMS deliverability.
Common Developer Mistakes 🛑
- Relying solely on isPossible()
- Assuming isValid() means the number is real
- Allowing VoIP numbers during user registration
- Validating only client-side
- Not running server-side checks before sending SMS
These mistakes cause onboarding failures, high SMS costs, and spam account creation.
The Production-Grade Solution: Add Real-Time Validation ⚡🔍
Why Real-Time Validation Is Essential
Modern applications require more than syntactical checks.
They need answers to:
- Is this number active right now?
- Who is the carrier?
- Is it mobile, landline, or VoIP?
- Is it safe for onboarding?
These are things a static library cannot do.
Use AbstractAPI for Real-Time Phone Verification ✨
AbstractAPI’s Phone Validation API provides:
- Real-time number existence checks
- Carrier lookup
- Accurate line type detection
- Fraud signals
- Deliverability confirmation
Example: Real-Time Validation
async function validateNumberInRealTime(phoneNumberString) {
const API_KEY = 'YOUR_ABSTRACTAPI_KEY';
try {
const response = await fetch(
`https://phonevalidation.abstractapi.com/v1/?api_key=${API_KEY}&phone=${phoneNumberString}`
);
const data = await response.json();
console.log(data.line_type);
console.log(data.is_valid_phone);
} catch (error) {
console.error('API Error:', error);
}
}
validateNumberInRealTime('+18005550199');
Comparison: libphonenumber vs. AbstractAPI 📊
The Perfect Workflow: Formatting + Client Checks + Server Validation (Working Together)
A robust phone-number experience isn’t about choosing formatting or validation — it’s about combining them into a layered workflow where each step does what it’s best at. Here’s the production-grade pattern most teams end up using:
1. Client-Side (UX Layer): Real-Time Formatting With AsYouType
At the point of entry, your user just needs help typing a readable number. This is where libphonenumber-js shines.
Using its AsYouType formatter, you can:
- Automatically add spaces, parentheses, or dashes as the user types
- Infer the country from input or use the device’s locale
- Prevent chaotic input (e.g., endless digits, strange punctuation)
- Provide a frictionless UI that feels “smart” without ever blocking the user
This layer is purely cosmetic, but it drastically reduces input errors and abandonment.
2. Client-Side (Light Validation): Instant Format Checks
Next comes the lightweight “early warning system.”
libphonenumber-js can tell you if the number appears valid — meaning:
- It has the correct number of digits for that country
- It uses a known prefix pattern
- It’s not something obviously malformed
This is not authoritative validation, but it helps you:
- Give real-time feedback (“This phone number doesn’t look right”)
- Disable the “Submit” button when the format is clearly broken
- Reduce round trips to your backend for garbage input
Think of this as the spellchecker, not the editor.
3. Server-Side (Authoritative Validation): The Final Decision With AbstractAPI
Once the form is submitted, it’s time for a definitive answer — not just “does this look like a phone?” but:
- Is it a real phone number that exists?
- Is it a mobile or landline? (Critical for SMS flows)
- Is it active and reachable?
- Does the carrier route support messaging?
- Did the user fake the country code?
This is where the AbstractAPI Phone Number Validation API steps in.
It performs a deep lookup using global numbering databases and carrier intelligence — something no client library can do.
This server-side check is the trust anchor for anything important:
- SMS verification
- Account creation
- 2FA
- Fraud reduction
- Customer support workflows
- Billing or transactional messaging
If formatting is the “nice UI handshake,” AbstractAPI is the security gatekeeper that ensures the user isn’t entering a disposable or invalid phone number.
Why This Workflow Works So Well
- Fast + smooth for the user
- Light on your backend
- Strong security and reliability
- No room for fake or unreachable numbers
- Prevents wasted SMS spend
- Minimizes fraud and spam behaviors
It’s the best of all worlds — and exactly the workflow used by most modern SaaS products, mobile apps, and signup flows.
Conclusion: The Tool Is Great — If You Know Its Limits 🎯
libphonenumber is an exceptional tool for formatting and syntactical checks.
It removes the complexity of global phone number structures and is perfect for user input handling.
But → isValid() does NOT mean the number exists.
To ensure accuracy, deliverability, and security, you must pair libphonenumber with a real-time validation service.
👉 Don’t just validate the pattern. Validate the number.
Get your free API key today:
https://www.abstractapi.com/phone-validation-api
FAQ ❓📘
What’s the difference between isPossible() and isValid()?
- isPossible() checks length.
- isValid() checks numbering rules.
Neither confirms real-world existence.
