Twilio makes HTTP requests to your application just like a regular web browser. By including parameters and values in its requests, Twilio sends data to your application that you can act upon before responding. You can configure the URLs and HTTP Methods Twilio uses to make its requests via the account portal or using the REST API.
Creating a Twilio Application within your account will allow you to more-easily configure the URLs you want Twilio to request when receiving a voice call to one of your phone numbers. Instead of assigning URLs directly to a phone number, you can assign them to an application and then assign that application to the phone number. This will allow you to pass around configuration between phone numbers without having to memorize or copy and paste URLs.
When Twilio receives a call for one of your Twilio numbers it makes a synchronous HTTP request to the Voice URL configured for that number, and expects to receive TwiML in response. Twilio sends the following parameters with its request as POST parameters or URL query parameters, depending on which HTTP method you've configured:
|CallSid||A unique identifier for this call, generated by Twilio.|
|AccountSid||Your Twilio account id. It is 34 characters long, and always starts with the letters AC.|
|From||The phone number or client identifier of the party that initiated the call. Phone numbers are formatted with a '+' and country code, e.g.
|To||The phone number or client identifier of the called party. Phone numbers are formatted with a '+' and country code, e.g.
|CallStatus||A descriptive status for the call. The value is one of
|ApiVersion||The version of the Twilio API used to handle this call. For incoming calls, this is determined by the API version set on the called number. For outgoing calls, this is the API version used by the outgoing call's REST API request.|
|Direction||A string describing the direction of the call.
|ForwardedFrom||This parameter is set only when Twilio receives a forwarded call, but its value depends on the caller's carrier including information when forwarding. Not all carriers support passing this information.|
|CallerName||This parameter is set when the IncomingPhoneNumber that received the call has had its
Twilio also attempts to look up geographic data based on the 'To' and 'From' phone numbers. The following parameters are sent, if available:
|FromCity||The city of the caller.|
|FromState||The state or province of the caller.|
|FromZip||The postal code of the caller.|
|FromCountry||The country of the caller.|
|ToCity||The city of the called party.|
|ToState||The state or province of the called party.|
|ToZip||The postal code of the called party.|
|ToCountry||The country of the called party.|
Depending on the what is happening on a call, other variables may also be sent. The individual TwiML verb sections have more details.
The following are the possible values for the 'CallStatus' parameter. These values also apply to the 'DialCallStatus' parameter, which is sent with requests to a
<Dial> Verb's action URL.
|queued||The call is ready and waiting in line before going out.|
|ringing||The call is currently ringing.|
|in-progress||The call was answered and is currently in progress.|
|completed||The call was answered and has ended normally.|
|busy||The caller received a busy signal.|
|failed||The call could not be completed as dialed, most likely because the phone number was non-existent.|
|no-answer||The call ended without being answered.|
|canceled||The call was canceled via the REST API while queued or ringing.|
After receiving a call, requesting TwiML from your app, processing it, and finally ending the call, Twilio will make an asynchronous HTTP request to the StatusCallback URL configured for the called Twilio number (if there is one). By providing a StatusCallback URL for your Twilio number and capturing this request you can determine when a call ends and receive information about the call. Non-relative URLs must contain a valid hostname (underscores are not permitted).
The parameters Twilio passes to your application in an asynchronous request to the StatusCallback URL include all those passed in a synchronous TwiML request.
The Status Callback request also passes these additional parameters:
|CallDuration||The duration in seconds of the just-completed call.|
|RecordingUrl||The URL of the phone call's recorded audio. This parameter is included only if Record=true is set on the REST API request, and does not include recordings from
|RecordingSid||The unique id of the Recording from this call.|
|RecordingDuration||The duration of the recorded audio (in seconds).|
All phone numbers in requests from Twilio are in E.164 format if possible. For example, (415) 555-4345 would come through as '+14155554345'. However, there are occasionally cases where Twilio cannot normalize an incoming caller ID to E.164. In these situations Twilio will report the raw caller ID string.
All dates and times in requests from Twilio are GMT in RFC 2822 format. For example, 6:13 PM PDT on August 19th, 2010 would be 'Fri, 20 Aug 2010 01:13:42 +0000'