Developers
SMS OTP Verification for Websites: A Step-by-Step Build Plan
Adding phone verification to a website looks like a weekend job, and the happy path is. The rest of the work is the limits, the failures and the cost control. This plan covers all of it, in the order to build it.
1. Decide what verification is for
- Reduce fake sign-ups.
- Protect high-risk actions.
- Recover accounts.
- Each aim needs different strictness.
2. The data you need
| Field | Why |
|---|---|
| user or session id | Link the code to a person |
| phone number in a standard format | Compare without formatting differences |
| code hash | Never store the code itself |
| expiry time | End the life of the code |
| attempt count | Stop guessing |
| created time | Rate limit and audit |
3. Send step
- Validate the number format first.
- Check rate limits before sending.
- Create the code and store the hash.
- Send through your message provider.
- Return a neutral response to the browser.
4. Check step
- Find the latest unused code for the session.
- Compare the hash.
- Count the attempt.
- Mark it used when it matches.
- Mark the phone number as verified.
5. Failure handling
- Show a clear message when the code expired.
- Provide a resend button with a timer.
- Offer another method when SMS fails.
6. Test before launch
Test with numbers from several countries. A virtual number lets you try the flow without using staff phones. See the SMS pumping guide for the limits that stop cost abuse.
Cost control
Every message costs money, and a form open to the internet attracts abuse. Count messages per day, set a budget and send an alert when it is reached.
After launch
- Review the failure reasons weekly.
- Check delivery rate by country.
- Remove countries you do not serve.
- Update the validation library.
Questions people ask
Do I need my own SMS gateway?
You need a provider that sends the messages. This guide is independent of the provider.
How do I stop fake sign-ups?
Rate limits, country rules and a bot check help most.
Related guides and pages
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