Webhooks

Webhooks Overview

How ThunderPhone delivers real-time events, how to verify signatures, and how the legacy and endpoint-based delivery models compare.

ThunderPhone sends HTTP POST requests to your server when things happen during a call — an inbound call starts, a call ends, a grading run completes, an alert fires, and so on. There are two delivery models:

All ten event types in the events catalog are delivered through webhook endpoints. The six call-lifecycle events (telephony.incoming, telephony.complete, telephony.tool, web.incoming, web.complete, web.tool) are also sent to the legacy single-URL webhook — if you have both a legacy URL and a matching endpoint, you receive the event on both paths. Blocking behavior (the telephony.incoming / web.incoming configuration exchange and webhook-mode tool dispatch) lives exclusively on the legacy path; every endpoint delivery is a fire-and-forget notification.

Payload format#

Endpoint deliveries are a JSON object with data, event_id, and type:

{
  "data": {
    "call_id": 987654321,
    "from_number": "+14155550199",
    "to_number": "+15551234567"
  },
  "event_id": "3f6b2ad0-1c9e-4a57-9f2b-8f6f0f9d2f11",
  "type": "telephony.incoming"
}

event_id is unique per emitted event. It is identical across retries and across every endpoint that receives the event — dedup on it.

The legacy single-URL webhook sends the same type and data but without event_id:

{
  "type": "telephony.incoming",
  "data": { "call_id": 987654321, "from_number": "+14155550199", "to_number": "+15551234567" }
}

On the wire, every body is serialized canonically — keys sorted alphabetically, no whitespace, UTF-8. The pretty-printed examples in these docs are for readability only.

See the Events catalog for the full list of event types and payload fields.

Signature verification#

Every request carries an HMAC-SHA256 signature over the raw request body in the X-ThunderPhone-Signature header. The signing key is the endpoint's secret (or your org-level webhook secret for legacy deliveries).

Steps#

1. Read the raw request body before any parsing.
2. Compute hmac_sha256(secret, body).hexdigest().
3. Compare in constant time to the X-ThunderPhone-Signature header.

We sign exactly the bytes we transmit, and those bytes are the canonical JSON serialization (sorted keys, compact separators). So verifying against the raw body always works — and if your framework only hands you parsed JSON, re-serializing it with sorted keys and compact separators produces the identical bytes. Both recipes are covered in the verification guide.

import hmac
import hashlib
 
def verify_signature(body: bytes, signature: str, secret: str) -> bool:
    expected = hmac.new(
        secret.encode("utf-8"),
        body,
        hashlib.sha256,
    ).hexdigest()
    return hmac.compare_digest(expected, signature or "")
 
# Example Flask handler
from flask import Flask, request, abort
app = Flask(__name__)
 
@app.post("/thunderphone-webhook")
def handle():
    body = request.get_data()
    sig = request.headers.get("X-ThunderPhone-Signature", "")
    if not verify_signature(body, sig, WEBHOOK_SECRET):
        abort(401)
    event = request.get_json()
    # dispatch on event["type"] …
    return "", 204

import crypto from "node:crypto";
import express from "express";
 
function verifySignature(body, signature, secret) {
  const expected = crypto
    .createHmac("sha256", secret)
    .update(body)
    .digest("hex");
  if (!signature || expected.length !== signature.length) return false;
  return crypto.timingSafeEqual(
    Buffer.from(expected),
    Buffer.from(signature),
  );
}
 
const app = express();
app.post(
  "/thunderphone-webhook",
  express.raw({ type: "application/json" }),
  (req, res) => {
    const sig = req.header("X-ThunderPhone-Signature") || "";
    if (!verifySignature(req.body, sig, process.env.WEBHOOK_SECRET)) {
      return res.sendStatus(401);
    }
    const event = JSON.parse(req.body.toString("utf8"));
    // dispatch on event.type …
    res.sendStatus(204);
  },
);

Delivery semantics#

These semantics apply to endpoint deliveries. The legacy single-URL webhook is a single synchronous attempt with no retries.

Choosing between legacy and endpoint-based webhooks#

New integrations should consume events through endpoint-based webhooks. Keep (or add) a legacy URL only if you configure calls dynamically at pickup time or use webhook-mode tool dispatch — those request/response exchanges only run on the legacy path.

Related#