# How do I build an OTP verification flow?

> Build an OTP flow in five steps: generate a short single-use code server-side, send it over a high-priority channel with a fallback, store a hashed copy with a short expiry, verify the user's input against it with attempt limits, and rate-limit requests to defend against pumping. Keep the code out of logs, never trust the client to validate, and prefer network-based verification where it removes the code entirely.

- Canonical URL: https://www.broadnet.me/answers/how-to-build-otp-flow
- Language: en
- Last reviewed: 2026-07-22
- Publisher: BroadNet (https://www.broadnet.me)

## Generate and store securely

Create a 4–8 digit code server-side, store only a hash of it with a short TTL (5–10 minutes), and bind it to the user and channel. Never send the code to the client for comparison — verify on the server. See /answers/what-is-otp.

## Send with a fallback

Deliver over a direct, high-priority route and configure a fallback channel (flash call, WhatsApp, or voice) so a delayed SMS does not block the user. See /answers/best-channel-for-otp and /answers/sms-fallback-strategy.

## Verify with limits

Check the user's input against the stored hash, cap attempts before forcing a resend, invalidate on success, and expire quickly. See /answers/sms-otp-best-practices.

## Rate-limit and monitor

Limit requests per number and per IP to resist SMS pumping, and watch for spikes to unusual destinations. Consider silent network authentication to avoid sending a billable code at all. See /answers/what-is-sms-pumping and /answers/what-is-silent-network-auth.

## Related

- [All answers](https://www.broadnet.me/answers)
- [Glossary](https://www.broadnet.me/answers)
- [What is OTP?](https://www.broadnet.me/answers/what-is-otp)
- [What is a verification flow?](https://www.broadnet.me/answers/what-is-a-verification-flow)
- [What are SMS OTP best practices?](https://www.broadnet.me/answers/sms-otp-best-practices)
- [What is the best channel for OTP delivery?](https://www.broadnet.me/answers/best-channel-for-otp)
- [OTP service](https://www.broadnet.me/products/otp)
- [MyOTP](https://www.broadnet.me/products/myotp)
- [Developer docs](https://www.broadnet.me/developers)