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Fax Compatibility XML is a set of actions defined in an XML document you can use to tell SignalWire what to do when you receive an incoming fax.


When a fax is sent to one of your SignalWire phone numbers, SignalWire looks up the Fax Compatibility XML document from the URL you configured, and reads the instructions you provided to determine what to do.

Fax Compatibility XML allows you to control what SignalWire will do when you receive an incoming fax.


SignalWire makes an HTTP request to your configured endpoint just like a regular web form submission (POST) or page load (GET). The request includes contextual information about the fax, allowing you to respond dynamically and fluidly to the fax to meet the needs of your application.

You can configure the endpoint URL and HTTP Method in your phone number settings panel on your SignalWire Dashboard, or via the REST API.

Request Parameters

SignalWire sends the following parameters, as either URL query parameters or POST parameters, to your endpoint when it receives a fax:

FaxSid stringA unique identifier for the fax.
AccountSid stringThe account that the fax was sent from.
To stringThe number or SIP URI the fax will be sent to.
From stringThe number or SIP URI the fax was sent from.
ApiVersion stringThe version of the SignalWire API.

Responding to SignalWire

An example of a Compatibility XML document that receives an incoming fax:

<?xml version="1.0" encoding="UTF-8"?>
<Receive action="/fax/received"/>

When a fax comes into one of your SignalWire phone numbers, SignalWire makes an HTTP request to the URL endpoint you configured for that number. Your response to that request instructs SignalWire on what to do next.

Responses to the HTTP request are in SignalWire Compatibility XML. SignalWire starts at the top of your XML document and executes your commands in order, from top to bottom.


Compatibility XML verbs and their attributes are case-sensitive, so using <receive> instead of <Receive> will result in an error.

StatusCallback when sending a fax

When sending a fax you can specify a StatusCallback URL. If you do so, your specified URL will receive POST requests with the following parameters:

RemoteStationId optionalThe transmitting subscriber identification (TSID) reported by the fax machine that sent in the fax.
FaxStatus optionalThe status of the fax.
OriginalMediaUrl optionalThe original URL passed when a fax is sent.
NumPages optionalThe number of pages received from a successful fax.
MediaSid optionalThe SID that uniquely identifies the fax media.
MediaUrl optionalThe media URL to request to retrieve incoming media.
ErrorCode optionalThe error code provides more information on a failed fax.
ErrorMessage optionalThe message explaining the reason for fax failure.