Prevent fraud and user drop-off with OTP SMS API

Deliver one-time passwords (OTP) and SMS verification codes globally within seconds. Our robust OTP API ensures reliable delivery and seamless integration for critical moments.

Start for free Explore OTP API documentation

Trusted by 17,759 businesses worldwide for secure verification

Why choose BulkGate for your OTP SMS API

Priority SMS routing – blue paper airplane speeding ahead of others

Reliable delivery for critical verification

Ensure critical verification codes reach users instantly with direct carrier connections and priority routing designed specifically for time-sensitive OTP messages and 2FA verification.

Global reach with local optimization

Deliver OTP codes reliably to 199 countries and regions with local carrier connections, optimal routing, and compliance with regional telecom standards.

Global SMS delivery – worldwide OTP verification code reach

Developer-friendly API integration for easy OTP implementation

Developer-friendly implementation

Integrate quickly using a clean REST API, comprehensive documentation, code examples, and dedicated OTP endpoints that simplify adding SMS verification to any application.

Cost-effective security solution

Prevent costly security breaches and abandoned signups with SMS verification that costs just cents per message while providing enterprise-grade protection.

Cost-effective OTP SMS security for affordable fraud prevention

What you can build with our OTP SMS API

Our versatile OTP SMS API lets you send secure SMS codes for a wide range of critical user interactions.

User authentication

Transaction security

Password recovery

POST /api/1.0/otp/send HTTP/1.1 Host: portal.bulkgate.com Content-Type: application/json Cache-Control: no-cache { "application_id": 451, "application_token": "YDbkJ5tXeZkqF48dCQEHiVMiK1m95atbhbn83CYHi0BareuraP", "number": "777777777", "country": "gb", "language": "en", "code_type": "string", "code_length": 4, "request_quota_number": 1, "request_quota_identification": "127.0.0.1", "trials_available_resend": 2, "trials_available_verification": 5, "daily_limit": 100, "daily_limit_country": {"cz": 150, "sk": 50}, "expiration": 3600, "channel": { "rcs": { "sender": "Rogue", "expiration": 100 }, "viber": { "sender": "Dakota Smith", "expiration": 100 }, "sms": { "sender_id": "gText", "sender_id_value": "Regina Jones", "unicode": true } } }

Simplify user registration and login

Build secure registration flows and two-factor authentication (2FA) systems that prevent fake accounts and unauthorized access with advanced rate limiting and fraud protection.

OTP Authentication API Guide

POST /api/1.0/otp/resend HTTP/1.1 Host: portal.bulkgate.com Content-Type: application/json Cache-Control: no-cache { "application_id": 451, "application_token": "YDbkJ5tXeZkqF48dCQEHiVMiK1m95atbhbn83CYHi0BareuraP", "id": "opt-id" }

Secure high-value transactions

Add an extra security layer for payments, transfers, and sensitive operations with instant SMS verification codes.

Transaction Security API Guide

POST /api/1.0/otp/verify HTTP/1.1 Host: portal.bulkgate.com Content-Type: application/json Cache-Control: no-cache { "application_id": 451, "application_token": "YDbkJ5tXeZkqF48dCQEHiVMiK1m95atbhbn83CYHi0BareuraP", "id": "opt-id", "code": "0451" }

Enable secure password recovery

Implement reliable password recovery flows that verify user identity via their registered phone number.

Password Recovery API Guide

Unlock powerful OTP API features

Core OTP actions Complete OTP lifecycle with three endpoints: `send` delivers configurable codes, `resend` automatically retries with throttling, `verify` validates codes with attempt tracking.

Advanced security controls Configure maximum verification attempts (e.g., fail after 4th wrong code), rate limiting between resends (minimum 1 minute), IP quotas for robust brute-force protection.

Customizable code rules Define code length (4–100), type (numeric/alphanumeric, case-insensitive), and expiration time. Localize messages by specifying a language (ISO code) for a global audience.

Multi-channel delivery with cascade Reach users via SMS, WhatsApp, Viber, or RCS with automatic channel failover to ensure OTP delivery even when the preferred channel fails.

WebOTP browser integration Enhance UX with seamless, automatic OTP code autofill from SMS directly into web forms.

Real-time status & webhooks Get instant delivery reports and verification status updates sent directly to your system.

Robust API protection and full budget control

Secure your OTP SMS API against misuse and unexpected costs. Our platform gives you the tools to protect your integrations and manage spending with confidence.

OTP API budget management interface for setting sending limits

Always within budget Set precise spending limits (daily, monthly, per country) and receive automatic alerts before you exceed your budget. Full control and peace of mind.

OTP SMS API token management dashboard for key and access control

Granular access management Securely manage different projects by creating dedicated API keys, each with its own permissions and spending limits.

OTP SMS API anti-fraud ochrana – graf monitoringu odesílacích vzorců

Automatic abuse protection Our platform actively protects you with automatic rate limiting, prevention of repeated OTP sends to the same number, and real-time suspicious activity monitoring.

Explore API security

Flexible integration options

Clean REST API

Use dedicated endpoints for speed and security. Easy integration via HTTP methods.

Learn more

Ready-to-use SDKs

Our PHP library simplifies working with OTP. Includes ready-made methods for code generation and validation.

Learn more

Advanced connectivity

For high-traffic applications, we offer direct SMPP connections with maximum throughput.

Partner with us

Are you a consultant, agency, developer, or SaaS provider? Leverage our robust OTP SMS API for your clients or products and unlock new revenue streams.

Learn more about partnerships

Start sending OTP SMS in minutes

Getting started with our OTP SMS API is simple.

Start now for free

Generate your unique API key in the portal

Send your first OTP SMS code using our simple API guide

Developer support & resources

We're committed to your integration success. Access a wealth of resources and get help when you need it.

Comprehensive OTP API documentation with guides and tutorials

Ready-to-use PHP SDK and code examples

Reliable technical support via email

Explore OTP on other channels

While SMS is the most universal choice, some scenarios can benefit from modern chat apps. Explore our other APIs for delivering OTP codes.

WhatsApp OTP

Deliver codes on the world's most popular chat app.

Explore WhatsApp API

Viber OTP

For cost-effective delivery on key markets.

Explore Viber API

RCS OTP

For branded messages in the native Android & iOS messaging environment.

Explore RCS API

Voice OTP

Deliver OTP via an automated voice call — no internet or app required.

Contact sales

Frequently asked questions (FAQ)

How fast is SMS verification via OTP API?

OTP messages receive priority treatment across our network and are typically delivered within 2–10 seconds globally. We use direct carrier connections and dedicated routing specifically optimized for time-sensitive verification codes.

How configurable are OTP codes?

OTP codes (one-time passwords) are highly configurable: code length from 4–100 characters, numeric or alphanumeric format (case-insensitive), custom expiration times, multiple languages for message localization, and various security parameters such as maximum attempts and resend limits.

How does the resend function work?

The `resend` endpoint automatically uses the same parameters as the original `send` request but with built-in safeguards: minimum 1-minute delay between resends, maximum 3 resends per request, and source monitoring to prevent abuse.

Can I send OTP codes via multiple channels?

Yes, our OTP API supports SMS, WhatsApp, Viber, RCS, and Voice OTP with intelligent cascade. You can configure fallback sequences (e.g., Viber → SMS) to ensure delivery regardless of the user's preferred or available channel.

What is WebOTP and how does it work?

WebOTP is a browser standard that enables automatic extraction of codes from SMS messages directly into web forms. Our OTP API supports this mechanism, enabling a seamless user experience where verification codes auto-fill without manual typing.

What security safeguards are built into the OTP SMS API?

Our OTP API provides multi-layered security protection:
Configurable limits: Maximum verification attempts per code (e.g., fail after 4th wrong code), mandatory delays between resends (minimum 1 minute), IP quotas for OTP requests, and maximum resends per original request (e.g., 3 times).
Built-in protection: Automatic code expiration handling, rate limiting per phone number for OTP requests, and priority routing to prevent security-compromising delays.
All these OTP-specific security measures are fully customizable to match your security requirements.

How fast is SMS verification via OTP API?

How to handle OTP delivery failures?

Our API provides real-time delivery status via webhooks. You can implement automatic retry logic, alternative delivery methods, or fallback verification mechanisms. We also provide detailed failure reasons to help improve delivery success rates.

Is the OTP SMS API suitable for high-volume applications?

Our infrastructure handles millions of OTP messages daily for large financial institutions and technology companies. For exceptionally high volumes, we offer enterprise-grade SMPP connectivity.

Ready to secure your applications with OTP SMS API?

Unreliable verification costs you users and trust. Join 17,759 businesses that use BulkGate's OTP SMS API for reliable and secure authentication.

Start for free Explore OTP API documentation