Turn a Twilio number into a programmable cloud call center with one .NET service.
TODO: add a short demo GIF showing
POST /api/calls/starttriggering a two-leg call flow with the resulting TwiML response inline.
Building a programmable call center on top of Twilio usually means buying a packaged solution or stitching together half a dozen webhook handlers by hand. This is the smallest .NET 8 service that proves you don't need either — one ASP.NET Core app handles call origination, IVR, status callbacks, and SMS, with signed Twilio webhooks and DI-friendly configuration out of the box.
It's a reference implementation, not a product. Read it, fork it, lift the parts you need.
Place a call between two phone numbers — Twilio dials the callee first, asks them to press a key to accept, then bridges the caller in.
curl -X POST http://localhost:5000/api/calls/start \
-H "Content-Type: application/json" \
-d '{
"correlationId": "demo-001",
"callerNumber": "+15555550001",
"calleeNumber": "+15555550002",
"maxDurationSeconds": 600
}'Behind the scenes:
- The service asks Twilio to call
calleeNumberfrom your Twilio number. - When the callee picks up, Twilio hits
/api/dtmfor IVR — a<Gather>plays a prompt and waits for a keypress. - On a keypress,
/api/connectreturns TwiML that<Dial>scallerNumber, bridging the call. /api/eventreceives status callbacks (initiated,ringing,answered,completed) and forwards them to your configured webhook.
git clone https://github.com/TheSmallPixel/TwilioCallCenter.git
cd TwilioCallCenter
# configure (use user-secrets, env vars, or appsettings.Development.json)
dotnet user-secrets init --project src/TwilioCallCenter
dotnet user-secrets set "Twilio:AccountSid" "ACxxxxxxxx" --project src/TwilioCallCenter
dotnet user-secrets set "Twilio:AuthToken" "xxxxxxxxxx" --project src/TwilioCallCenter
dotnet user-secrets set "Twilio:FromNumber" "+15551234567" --project src/TwilioCallCenter
dotnet user-secrets set "CallCenter:PublicBaseUrl" "https://your-tunnel.ngrok.io" --project src/TwilioCallCenter
dotnet run --project src/TwilioCallCenterThen point your Twilio number's webhook to https://<your-public-url>/api/dtm and you're live.
- Live demo — none; this is a reference implementation
- Changelog — CHANGELOG.md
- Contributing — CONTRIBUTING.md
- ASP.NET Core minimal hosting; DI'd configuration via
IOptions<TwilioOptions>andIOptions<CallCenterOptions> - Twilio webhook signature validation enforced on every callback (
X-Twilio-Signature) - IVR (
<Gather>), bridging (<Dial>), status callbacks, and SMS in five controllers IHttpClientFactory-based status forwarding — async, no socket exhaustion- xUnit test suite covering TwiML output and signature validation
POST /api/calls/start → Twilio originates outbound call
└─→ /api/dtm (TwiML: Gather + prompt)
└─→ /api/connect (TwiML: Dial caller)
└─→ /api/event (status callbacks)
POST /api/sms → Twilio sends an SMS
| Key | Required | Description |
|---|---|---|
Twilio:AccountSid |
yes | Twilio Account SID |
Twilio:AuthToken |
yes | Twilio auth token (used both for the REST client and signature validation) |
Twilio:FromNumber |
yes | E.164 number that calls and SMS originate from |
CallCenter:PublicBaseUrl |
yes | Public HTTPS base URL Twilio can hit (ngrok in dev, your domain in prod) |
CallCenter:StatusWebhookUrl |
optional | URL the service POSTs call status updates to |
CallCenter:GreetingText |
optional | Voice prompt played to the callee before the keypress |
CallCenter:ConnectingText |
optional | Voice prompt played right before bridging |
CallCenter:Voice |
optional | Twilio TTS voice (default alice) |
CallCenter:Language |
optional | TTS language (default en-US) |
dotnet build
dotnet test
dotnet run --project src/TwilioCallCenter- Persist call state to Redis or SQL (
IMemoryCacheis fine for a single-instance reference) - Recording + transcription endpoints
- OpenAPI / Swagger UI for the public surface
MIT © Lorenzo Longiave