Twilio is a communications platform made by Twilio Inc. It offers APIs (interfaces that other programs call over the internet) through which an application sends and receives text messages, voice calls and email, and checks a user's identity.
With Programmable Messaging, a program makes one API call with a sender number, a recipient number and a text, and Twilio delivers it as SMS, MMS (a message with images or other media), RCS (rich messages with cards and read receipts) or WhatsApp. Incoming replies reach the application through a webhook: an address on the application's server that Twilio calls with the message. A business leases phone numbers from Twilio: long codes (normal 10-digit numbers), toll-free numbers, or short codes of 5 or 6 digits for high volumes. Other products handle voice calls, email through Twilio SendGrid, one-time passcodes through Verify, and voice AI agents through Conversation Relay.
Twilio is a hosted service billed per use, with no contract: each message segment and each leased number has a price, with discounts at higher volume. A free trial needs no credit card.