Verify Users with
SMS Codes
Send verification codes to phone numbers worldwide. Reduce fraud, verify identity, and secure user accounts with SMS OTP. See SMS pricing.
Free tier · No credit card required
import Zavudev from '@zavudev/sdk'
const zavu = new Zavudev({ apiKey: process.env.ZAVUDEV_API_KEY })
// Send a verification code — SMS with WhatsApp fallback
await zavu.messages.send({
to: '+14155551234',
channel: 'auto',
fallbackEnabled: true,
text: 'Your verification code is 481920.',
})Why Zavu
Why SMS Verification?
A failed verification is a lost signup. Every code is optimized for delivery, cost, and trust.
Prevent Fraud
Verify that users control the phone numbers they claim, reducing fake accounts and fraud.
Fast Delivery
OTP codes delivered in seconds with our optimized SMS infrastructure.
Global Coverage
Verify phone numbers in 200+ countries with localized sender IDs.
Lower cost
Smart routing picks the cheapest route that still delivers, so you pay the floor for that destination.
Live in minutes
One send() call, with SDKs for Node, Python, Ruby, Go, and Java.
Secure
Cryptographically secure code generation with configurable expiry times.
How it works
How SMS Verification Works
Send Code
User enters phone number, you send a verification request to our API.
User Receives
We deliver a unique OTP code to the user's phone via SMS.
Verify
User enters the code, you verify it against our API.
Anti-fraud
Stop fake accounts before they start.
Verification only helps if it's hard to game. Fraud protection is on by default.
SMS pumping protection
Detect and block artificial traffic inflation.
Rate limiting
Cap requests per number and per window.
Auto expiry
Codes expire on a schedule you control.
One-time use
Codes invalidate after a successful check.
Use cases
Common Use Cases
FAQ
Questions, answered.
How fast do codes arrive?
Median delivery is a few seconds on SMS and sub-second on WhatsApp. We route each code to the fastest path for the destination country.
What if a message fails to deliver?
With fallback enabled, Zavu retries on another channel automatically so the code still lands and you don't lose the signup.
How much does it cost?
Start free with 2,000 messages a month. Smart routing always picks the lowest-cost path that still delivers, and we never markup carrier fees.
Do you prevent SMS pumping fraud?
Yes. Rate limiting, geo controls, and routing rules block artificial traffic inflation before it hits your bill.
How long does integration take?
Minutes. It's one send() call, with SDKs for five languages and a REST API. No contracts, no minimums.
What is an SMS verification API?
An SMS verification API sends a one-time code to a phone number and confirms the person entering it controls that number. You call one endpoint, the provider handles code generation, delivery, expiry and retries. It is the standard way to stop fake signups without adding friction.
What is an OTP API and how do I add one?
An OTP API issues and validates one-time passcodes. With Zavu it is a single send call with the code you generated, or your own logic on top. You keep control of code length, expiry and retry policy instead of inheriting a black box.
How do I add two-factor authentication to my app?
Send a one-time code to the user's phone at login, then verify what they type back. That is a 2FA API in one sentence. The engineering that follows is delivery reliability, rate limiting and fraud controls, which is the part worth buying rather than building.
Is SMS OTP safe, or should I use an authenticator app?
Authenticator apps are more secure because they resist SIM swap and interception. SMS wins on reach: everyone has it, nothing to install, no recovery flow to support. Most products offer SMS as the default and an authenticator app as an upgrade for accounts worth attacking.
Ready to Verify Users?
Start verifying phone numbers in minutes. No contracts, no minimums.