Relay | SignalWire

The Relay namespace provides imperative, event-driven control over voice calls and SMS/MMS messages through a persistent WebSocket connection to SignalWire. While the Agents namespace handles AI-driven conversations declaratively via SWML, Relay gives you fine-grained, async control over every step of a call — answering, playing prompts, collecting digits, recording, bridging, conferencing, and more.

Relay uses the JSON-RPC 2.0 protocol over WebSocket (wss://). The client authenticates once, subscribes to contexts for inbound events, and processes call and message events in an async event loop. Automatic reconnection with exponential backoff ensures resilience against transient network failures.

Context Routing

Contexts are routing labels that control which inbound calls and messages are delivered to your application. When you assign a phone number to a context in the SignalWire dashboard, all calls to that number are routed to Relay clients subscribed to that context.

from signalwire.relay import RelayClient
# Subscribe to specific contexts
client = RelayClient(
    project="your-project-id",
    token="your-api-token",
    contexts=["support", "sales"],
)
@client.on_call
async def handle_call(call):
    await call.answer()
    # Or subscribe/unsubscribe dynamically
    # await client.receive(["billing"])     # Add a context
    # await client.unreceive(["sales"])     # Remove a context
client.run()

A client only receives events for its subscribed contexts. This enables multiple applications or workers to handle different call flows on the same project by subscribing to different contexts.

Example

An IVR that answers calls, plays a menu, collects a digit, and routes accordingly:

from signalwire.relay import RelayClient
client = RelayClient(
    project="your-project-id",
    token="your-api-token",
    contexts=["default"],
)
@client.on_call
async def handle_call(call):
    await call.answer()
    # Play a menu and collect one digit
    action = await call.play_and_collect(
        media=[{"type": "tts", "params": {"text": "Press 1 for sales, 2 for support."}}],
        collect={"digits": {"max": 1, "digit_timeout": 5.0}},
    )
    event = await action.wait()
    digit = event.params.get("result", {}).get("digits", "")
    if digit == "1":
        await call.play([{"type": "tts", "params": {"text": "Transferring to sales."}}])
        await call.transfer(dest="+15551234567")
    elif digit == "2":
        await call.play([{"type": "tts", "params": {"text": "Transferring to support."}}])
        await call.transfer(dest="+15559876543")
    else:
        await call.play([{"type": "tts", "params": {"text": "Goodbye."}}])
        await call.hangup()
client.run()

Classes

RelayClient

WebSocket client for connecting, authenticating, dialing calls, and sending messages.

Call

Call object with methods for answer, hangup, play, record, collect, connect, and more.

Message

Message object for tracking SMS/MMS state and waiting for delivery confirmation.

Actions

Async action handles returned from call control methods like play, record, and detect.

Events

Typed event dataclasses for call state changes, playback, recording, and messaging.

Constants

Call states, connect states, message states, and event type string constants.

RelayError

Exception raised when the Relay server returns an error response.