ElevenLabs Webhooks & Events

Overview

ElevenLabs webhooks send HTTP POST notifications when async operations complete: transcription completion, post-call data from Conversational AI agents, and call initiation failures. Every delivery is signed with an HMAC-SHA256 signature you must verify before processing. This skill builds a secure endpoint that verifies signatures, routes events by type, and acks fast to avoid auto-disable.

Prerequisites

• ElevenLabs account (webhooks configured in Settings > Webhooks)
• HTTPS endpoint accessible from the internet
• Webhook secret (generated during webhook creation in dashboard)

Instructions

The full, copy-ready code for each step lives in references/implementation.md; per-event handlers live in references/examples.md. The high-level workflow:

1. Know the event types — subscribe only to what you handle (table below).
2. Create the webhook in the dashboard (Settings > Webhooks) and copy the HMAC secret.
3. Verify the signature with HMAC-SHA256 over "<timestamp>.<raw_body>", using a timing-safe compare and a 5-minute replay window. See the full verifier.
4. Handle the request with a raw body parser, ack 200 immediately, then process asynchronously. See the Express handler.
5. Route events to per-type handlers. See handler examples.
6. Guard against duplicates with idempotency keyed on the event ID. See idempotency.
7. Test locally by tunneling with ngrok. See local testing.

Webhook event types

Event Type	Payload	When Triggered
post_call_transcription	Full conversation transcript, analysis, metadata	After Conversational AI call ends
post_call_audio	Base64-encoded call audio, minimal metadata	After call ends (if audio recording enabled)
call_initiation_failure	Failure reason, metadata	When an outbound call fails to connect
speech_to_text.completed	Transcription result, word timestamps	Async STT job completes

Signature verification skeleton

// src/elevenlabs/webhook-verify.ts — Header: t=<unix_ts>,v1=<hex_sig>
export function verifyWebhookSignature(rawBody, signatureHeader, secret) {
  const parts = new Map(signatureHeader.split(",").map(p => {
    const [k, ...v] = p.split("="); return [k, v.join("=")];
  }));
  const timestamp = parts.get("t"), signature = parts.get("v1");
  if (Math.floor(Date.now() / 1000) - parseInt(timestamp) > 300) {
    return { valid: false, reason: "Timestamp too old" };   // replay guard
  }
  const expected = crypto.createHmac("sha256", secret)
    .update(`${timestamp}.${rawBody.toString()}`).digest("hex");
  return { valid: crypto.timingSafeEqual(
    Buffer.from(signature, "hex"), Buffer.from(expected, "hex")) };
}

See references/implementation.md for the production-hardened version with full error handling.

Output

Applying this skill produces:

• src/elevenlabs/webhook-verify.ts — reusable HMAC-SHA256 verifier with replay protection and timing-safe comparison.
• src/api/webhooks/elevenlabs.ts — Express route that verifies signatures, acks 200 immediately, and routes events to per-type handlers.
• Per-event handler functions (handleTranscription, handleCallAudio, handleCallFailure, handleSTTCompleted) extracting the fields each payload carries.
• An idempotency wrapper keyed on event ID so retried deliveries are processed once.

At runtime a verified delivery returns { "received": true } with HTTP 200; a bad signature or expired timestamp returns HTTP 401 { "error": "Invalid signature" }.

Webhook Reliability

Behavior	Detail
Retry policy	ElevenLabs retries failed deliveries
Auto-disable	After 10 consecutive failures AND 7+ days since last success
Timeout	Your endpoint must respond within a few seconds
Re-enable	Manually re-enable in dashboard after fixing the endpoint
Authentication	HMAC-SHA256 via ElevenLabs-Signature header

Error Handling

Issue	Cause	Solution
Signature mismatch	Wrong secret or body parsing	Use express.raw(), verify secret matches dashboard
Webhook auto-disabled	10+ consecutive failures	Fix endpoint, re-enable in dashboard
Duplicate events	Retried delivery	Implement idempotency with event ID tracking
Handler timeout	Slow processing	Return 200 immediately, process async
Replay attack	Old timestamp reused	Check timestamp age (reject > 5 min)

Examples

Route a decoded event to the right handler:

switch (event.type || event.event_type) {
  case "post_call_transcription": await handleTranscription(event); break;
  case "post_call_audio":         await handleCallAudio(event);     break;
  case "call_initiation_failure": await handleCallFailure(event);   break;
  case "speech_to_text.completed": await handleSTTCompleted(event); break;
  default: console.log("Unhandled event type:", event.type);
}

Simulate a delivery locally with curl:

curl -X POST http://localhost:3000/webhooks/elevenlabs \
  -H "Content-Type: application/json" \
  -H "ElevenLabs-Signature: t=$(date +%s),v1=test" \
  -d '{"type":"speech_to_text.completed","data":{"text":"Hello world"}}'

Full per-event handlers (transcript, audio, call-failure, STT) with the exact fields each payload carries are in references/examples.md.

Resources

• Post-Call Webhooks
• Webhook API Reference
• references/implementation.md — full verifier, Express handler, idempotency, ngrok testing
• references/examples.md — per-event handler examples

Next Steps

For performance optimization, see the elevenlabs-performance-tuning skill, which covers connection pooling and batching to keep webhook handlers fast enough to ack within the ElevenLabs timeout window.