SMS gateway API: what it is and how it works
An SMS gateway API is the web interface a business SMS provider publishes so that software sends and receives text messages through the provider's connection to the mobile carriers. In the documentation of the providers we assess, sending one text is one HTTPS POST request carrying the recipient, the sender and the message text, authenticated with account credentials or an API key. Delivery status comes back by webhook, with the provider posting each status change to a URL you set.
Alain Grossbard OAM, with Justin Grossbard Updated How we rate Reader supported, we may earn a commission Reader supported. We may earn a commission when you sign up through a link on this page, and it never changes a score. How we make money.
What the 15 APIs document
The table below counts what the 15 SMS gateway APIs we assess document, criterion by criterion, read from each provider's developer documentation on 21 September 2026. All 15 document a REST endpoint for sending and delivery receipts by webhook, 12 run a public status page, 11 publish official SDKs and 10 publish an uptime SLA. The two thinnest columns are the sandbox, test mode or test credentials, which 4 offer, and the published US throughput or rate limit, which 5 publish. For cost, the price ranking of the SMS APIs carries the numbers.
| What a developer checks | Documented | Partly | Not documented |
|---|---|---|---|
| Documented REST API for sending SMS | 15 of 15 | 0 | none |
| Delivery receipts by webhook | 15 of 15 | 0 | none |
| Public status page | 12 of 15 | 0 | Clickatell, SMSGlobal and BulkSMS |
| Official SDKs | 11 of 15 | 3 | none not read: Kudosity |
| Published uptime SLA | 10 of 15 | 1 | Bird, Messente, SMSGlobal and BulkSMS |
| US 10DLC, toll-free and short code numbers | 10 of 15 | 1 | Messente, SMSGlobal, BulkSMS and Notifyre |
| Published US throughput or rate limit | 5 of 15 | 6 | Clickatell, Bird, BulkSMS and Notifyre |
| Sandbox, test mode or test credentials | 4 of 15 | 4 | Plivo, Bandwidth, Bird and BulkSMS not read: Kudosity, Notifyre and Vonage |
"Partly" means the documentation covers the point for some products or number types and not others; each provider's reading, with the quote behind it, is on the best SMS APIs, and the eight criteria are set out on how we rate SMS providers.
How an SMS gateway API works
Get credentials and a sending number
You get an API key or account credentials and a sending number from your provider. A US business sending from a local ten digit number registers its brand and each campaign for 10DLC with The Campaign Registry through that provider, at $4.50 to register a brand and $10 a month per standard campaign per TCR's fee schedule, read 21 September 2026. The full 10DLC fees are on our registration page.
Send the request
Your software sends one HTTPS POST request to the provider's endpoint. Twilio documents a POST to its Messages resource with HTTP Basic authentication and the fields To, From and Body. Telnyx documents a POST to https://api.telnyx.com/v2/messages with a Bearer API key in the Authorization header and the fields from, to and text, both read 21 September 2026.
Receive status and replies by webhook
The provider posts each delivery status change to a webhook URL you set, so your software learns each status change. Replies from recipients arrive the same way, as a request to that webhook URL. Twilio and Telnyx both document this webhook flow, read 21 September 2026.
Choose by what the documentation states
All 15 SMS gateway APIs we assess document a REST endpoint for sending and delivery receipts by webhook, read from each provider's developer documentation on 21 September 2026. The ranked comparison puts each provider's send request side by side.