# What are SMS OTP best practices?

> Deliver SMS one-time passwords over a dedicated high-priority route, keep codes short (4–8 digits), expire them quickly (typically 5–10 minutes), enforce single use, and rate-limit requests per number to defend against SMS-pumping fraud. Put the brand name and the code near the start of the message, include no clickable links (so the message can't be confused with phishing), and configure a fallback channel for when SMS is slow. See /products/otp.

- Canonical URL: https://www.broadnet.me/answers/sms-otp-best-practices
- Language: en
- Last reviewed: 2026-07-22
- Publisher: BroadNet (https://www.broadnet.me)

## Code design and lifetime

Use 4–8 numeric digits — long enough to resist guessing, short enough to type. Set a short expiry (5–10 minutes), invalidate the code after one successful use, and cap verification attempts before forcing a resend. See /answers/what-is-otp and /answers/what-is-2fa.

## Defend against SMS pumping (AIT)

Artificially Inflated Traffic — fraudsters triggering floods of OTPs to premium numbers to earn a cut of the traffic — can quietly dominate an OTP bill. Rate-limit per number and per IP, add velocity checks, and monitor sudden spikes to unusual country codes. See /answers/what-is-sms-pumping and /answers/what-is-ait.

## Speed and route priority

OTP is time-sensitive: a code that arrives after the user gives up is a failed login. Send OTP over direct, high-priority routes with headroom for bursts, and monitor DLRs so you catch route degradation before users do. See /answers/what-is-dlr.

## Add a fallback channel

If SMS is delayed in a market, fall back automatically to flash-call verification, WhatsApp, or voice OTP so conversion doesn't depend on one channel. See /answers/what-is-flash-call-verification and /answers/what-is-silent-network-auth.

## Message content and anti-phishing

Lead with your brand and the code, state what it is for, and include no links — legitimate OTP messages never ask the user to click. This trains users to distrust OTP-style messages that do contain links. See /answers/what-is-smishing.

## 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 2FA (two-factor authentication)?](https://www.broadnet.me/answers/what-is-2fa)
- [What is SMS pumping / artificial inflated traffic (AIT)?](https://www.broadnet.me/answers/what-is-sms-pumping)
- [What is Flash Call verification?](https://www.broadnet.me/answers/what-is-flash-call-verification)
- [OTP service](https://www.broadnet.me/products/otp)
- [MyOTP](https://www.broadnet.me/products/myotp)