SMS Testing · OTP · Mock SMS API · Staging
Test SMS OTP Delivery Without Real Carriers or Real Credits
Zunoy SMS Inbox is a mock SMS API for staging environments — replace your real SMS gateway with one endpoint change and every OTP your app sends lands in a shared team inbox instead of a real carrier. Test OTP without sending SMS to anyone. No credits burned. No real numbers contacted. Full payload visible to your whole team.
Works with Twilio · MSG91 · Exotel · AWS SNS · Fast2SMS · Textlocal · Any REST SMS gateway
If you're looking for any of these, this page is for you
Zunoy SMS Inbox is a mock SMS API built for development and staging teams. Your app sends the same request it always has — Sandbox receives it, logs the full payload, and makes it instantly visible to your team. No carrier involved. No credits consumed.
Testing SMS OTP flows in staging is expensive, messy, and unreliable.
You're Burning Real SMS Credits on Staging Tests
Every OTP your app sends during development goes to a real carrier — and costs real money. Your team burned through ₹3,000 in SMS credits last sprint. Testing. In staging. None of it reached a real user who needed it.
Your Test Numbers Are Hardcoded and Fragile
You've hardcoded a handful of test phone numbers and hope the OTP doesn't fire in production. When a number changes, or a developer in a different region tries to test, the whole flow breaks. There's no SMS sandbox API to catch what your app actually sent.
You Can't See What the Carrier Actually Received
Your app fires the SMS request. Your logs say success. But you have no way to see the actual message body, the Sender ID, the DLT template rendering, or the headers your app sent — so when something breaks, you're debugging blind.
Replace your SMS gateway with a mock SMS API. Every OTP lands in your inbox instead.
Swap your gateway URL for a mock SMS API endpoint
In your staging config, replace your SMS provider's base URL with your Zunoy SMS Inbox endpoint — turning Sandbox into a mock SMS API for your entire development environment. Your app sends the exact same API call — same body, same headers, same Sender ID. The OTP lands in Sandbox instead of a real carrier. Zero credits consumed. One environment variable changed.
Full payload inspection — every field your app sent
Every SMS in your inbox shows the complete payload — recipient number, Sender ID, message body, custom headers, and timestamp. See exactly what your app sent to the mock SMS gateway, not just that it sent something. The difference between "it worked" and "it worked correctly."
Validate Sender ID, DLT template, and message format
Confirm your Sender ID is correct, your OTP is formatted as expected, and your message body matches your registered DLT template — before a single real user receives an OTP from a real carrier.
Your whole team sees every OTP in real time
No more "did the OTP fire?" over Slack. Every team member sees every SMS the moment it arrives — Sender ID, recipient, body, headers, and timestamp — in the shared SMS sandbox inbox simultaneously.
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SMS testing in staging — configured in under 5 minutes.
Create an SMS inbox and get your endpoint
Create a project in Zunoy Sandbox. You get a unique REST API endpoint — your mock SMS API for this environment. Each inbox is isolated with its own credentials.
Replace your gateway URL
In your staging environment config, swap your SMS provider's base URL with your Zunoy SMS Inbox endpoint. Everything else — headers, payload structure, Sender ID, authentication — stays exactly the same. This is what makes Sandbox a true drop-in mock SMS API.
Trigger your OTP flow
Developer or QA triggers a login, signup, or verification flow. The app fires the same API call it always has — now pointing at your mock SMS gateway instead of a real carrier.
OTP lands in your SMS sandbox inbox
Full SMS payload appears in the shared inbox instantly — Sender ID, recipient number, message body, custom headers. Every team member sees it simultaneously. No phone. No credits. No carrier.
Validate and sign off
QA confirms the Sender ID matches the expected value. Checks OTP format and length. Verifies the message body matches the registered DLT template. Confirms headers pass validation. Issues found — developer fixes, retriggers, QA signs off.
One endpoint change. Your mock SMS API is ready.
Replace your real SMS gateway base URL with your Zunoy endpoint. Same payload structure. Same headers. Works with any REST SMS gateway.
Your real SMS provider and Zunoy SMS Inbox accept the same payload structure. This is a true mock SMS API — one environment variable changed, zero code changes, zero credits consumed.
curl --request POST \
--url https://sms.sandbox.zunoy.com/v1/send \
--header 'Authorization: Bearer YOUR_PROJECT_TOKEN' \
--header 'Content-Type: application/json' \
--data '{
"to": "+919876543210",
"sender": "FNTKBK",
"body": "Your OTP is 483920. Valid for 10 minutes. Do not share."
}'Every alternative costs you something — credits, visibility, or reliability.
Real SMS gateway in staging
Burns real credits on every test. Sends real OTPs to real numbers. No way to inspect the full payload the carrier received. Expensive, risky, and unscalable.
Hardcoded test numbers
Fragile. Numbers change. Regional teams can't test. You still can't inspect the Sender ID, DLT template rendering, or headers your app sent.
Disabling SMS entirely
You confirm nothing. Sender ID, template format, header validation — all untested. You find out what's wrong when real users report it.
Building an internal mock SMS API
Engineering time spent on infrastructure instead of product. Maintenance overhead. Still doesn't give you team-shared visibility or DLT template testing.
Zunoy SMS Inbox is a production-grade mock SMS API for staging — built, maintained, and ready in under 5 minutes. No internal tooling required.
BUILT FOR
Who uses Sandbox for SMS OTP testing
Backend developers
Replace your SMS gateway URL with a mock SMS API endpoint in staging. Every OTP your app sends lands in Sandbox — full payload visible, Sender ID confirmed, zero credits consumed. SMS testing in staging that takes 60 seconds to configure.
QA engineers
Validate Sender ID, OTP format, message body, and DLT template rendering on every SMS — in a shared SMS sandbox inbox your whole team sees simultaneously. No real phone number. No carrier dependency.
Mobile developers
Test the complete OTP login flow — request, delivery, format, expiry — on any device, without a real carrier or real phone number in the loop. Use the SMS sandbox API to simulate exactly what your users will receive.
Other testing scenarios covered by Sandbox
Transactional email testing
Capture, preview, and score every transactional email before it reaches a real user.
OTP / 2FA testing
Generate and verify TOTP codes in staging without real authenticator apps.
Webhook testing
Inspect, replay, and debug incoming webhook payloads with a persistent request log.
The things developers ask about SMS OTP Testing
What is a mock SMS API and how does Zunoy work as one?
A mock SMS API is a replacement endpoint that accepts your app's SMS requests without forwarding them to a real carrier. Zunoy SMS Inbox acts as your mock SMS API in staging — receiving every OTP your app sends, logging the full payload including Sender ID and headers, and making it instantly visible to your team. No real SMS is sent. No credits consumed. Configure it with one environment variable change.
How do I test OTP without sending SMS to real users?
Replace your SMS gateway's base URL with your Zunoy SMS Inbox endpoint in your staging environment config. Your app fires the same request — Sandbox receives it as a mock SMS gateway. Every OTP lands in your inbox instead of a real carrier. Full payload visible. Zero real numbers contacted. This is SMS testing in staging without any carrier involvement.
Does Sandbox work as an SMS sandbox API for Indian providers like MSG91 or Exotel?
Yes. Zunoy SMS Inbox works as an SMS sandbox API for any REST-based SMS gateway — MSG91, Exotel, Fast2SMS, Textlocal, Twilio, and any other provider. Replace the base URL in your config — same payload structure, same headers, same Sender ID. Works immediately.
Can I test DLT template rendering without a real carrier?
Yes. Create a template in Sandbox with your message body and variable placeholders — exactly like a DLT-registered template. Your app sends the template ID and variable values — Sandbox resolves and renders the full message in your SMS sandbox inbox. Test your DLT integration without carrier approval or real SMS costs. See SMS Inbox for full details.
Can I validate that my app is sending the correct headers to the mock SMS gateway?
Yes. Use Predefined Headers to define the headers your SMS requests must include. Requests with missing or incorrect headers are rejected by Sandbox — exactly like a real carrier would reject them. Catch header contract breaks in staging before they cause carrier rejections in production. See SMS Inbox for details.
Every Testing Scenario, One Sandbox Workspace
Your app sends emails, SMS, webhooks, and TOTP codes. Sandbox handles all four — in one workspace, under one account, visible to your whole team.
Email Inbox
SMS Inbox
Webhook Inbox
TOTP Inbox
Sandbox
Test Email, SMS, Webhooks & 2FA codes without touching production.
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