What it does
The Twilio MCP gives an agent the ability to send and receive text messages and voice calls through a Twilio account. It's the primary tool an Onyx deployment uses for any business that talks to customers over the phone — which is almost all of them.
Capabilities
- Send SMS and MMS from configured numbers
- Receive inbound SMS via webhook and route to the agent's conversation engine
- Place outbound voice calls (with text-to-speech or pre-recorded audio)
- Receive inbound voice calls and route to voicemail, the agent, or a human
- Look up phone number metadata (carrier, type, do-not-call status)
Authority surface
Like all communications MCPs, Twilio operates inside a defined authority surface:
- Allowed outbound numbers / number pools
- Allowed time windows (no SMS at 3am unless explicitly opted in)
- Per-customer opt-in tracking
- Rate limits (no more than N outbound to the same number in a day)
Auth
Account SID and Auth Token, scoped via subaccounts where multiple businesses are sharing infrastructure.
When to use it
- Onyx deployments that handle customer phone interactions
- Workflows like Missed Call Response that need an SMS leg
- Outbound qualification on a configurable cadence
Limitations
Does not provide WhatsApp or RCS (Twilio supports these, but the MCP is SMS / voice only for v1). Country availability varies by Twilio coverage.