Real-number services like Mailosaur and MailSlurp receive real texts on rented phone numbers, so they test carrier delivery. otpmock never sends a text: it catches the message at your provider's API, so it is faster, has unlimited fake numbers for parallel tests and is unaffected by carrier filtering, but it does not test delivery. Many teams use both for different jobs.
The core difference
With a real-number inbox, your app sends a real SMS through your real provider to a phone number the service owns. The service reads the text and exposes it over an API. With otpmock, your app's SDK talks to otpmock instead of the provider; the message is stored and never reaches a carrier.
Side by side
| Real-number inbox | otpmock | |
|---|---|---|
| Tests carrier delivery | Yes | No |
| Provider charges per test message | Yes | No |
| Time from send to readable code | Seconds, depends on carrier | Usually under a second |
| Numbers for parallel tests | The numbers you rent | Any fake number, one per test |
| Affected by carrier filtering of OTP traffic | Can be | No |
| Provider Verify APIs (code generated by provider) | Works, via real delivery | Emulated for Twilio, Vonage, Telnyx, Infobip, Sinch, Plivo, Telesign, Bird |
| Email testing | Yes, their main product | No, SMS only |
| Change in your app | None | One SDK option in test environments |
When a real-number inbox is the right tool
- You need proof that texts actually arrive, for example after changing sender IDs or templates.
- You test a third-party app where you cannot change the SMS client.
- You already use the same service for email testing and SMS is a small part of your suite.
When otpmock fits better
- OTP steps run on every login in a large E2E suite and speed matters.
- Tests run in parallel and sharing a few phone numbers causes collisions.
- You want zero provider charges and no exposure to carrier filtering in CI.
- You use a regional provider such as Netgsm, İleti Merkezi, Verimor or Mutlucell.
FAQ
Can I use both?
Yes. A common split is otpmock for the main suite and a real-number inbox for a nightly delivery check.
Does otpmock test emails?
No. otpmock is SMS only. Use an email testing service for email flows.
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