Testing SMS Verification as a Developer
How developers can test sign-up and login flows that depend on SMS codes, and best practices for building them.
If you build an app with phone verification, you need to test it constantly — but using your own number dozens of times a day is impractical and pollutes your inbox.
Use provider test modes first
Most SMS APIs offer test credentials and magic numbers that simulate delivery without sending real messages. Start there for automated tests.
Test real delivery with temporary numbers
To confirm messages actually arrive across countries and carriers, a temporary number lets you see the real message as a user would, including formatting and delay.
Design good OTP flows
Keep codes short-lived, limit attempts, add a resend cooldown, and show a clear countdown. Support autofill on mobile by following platform SMS formatting rules.
Offer alternatives
Not every user can receive SMS reliably. Email codes, authenticator apps or passkeys make your app more accessible and more secure.
More guides
- What Is a Virtual Phone Number?
- How OTP Verification Works
- Why Your OTP Is Not Coming (and What to Try)
- 10 Simple Ways to Protect Your Privacy Online