# Retell AI Webhooks

## When to Use This Skill

* How do I receive Retell AI webhooks?
* How do I verify Retell webhook signatures (`X-Retell-Signature`)?
* How do I handle `call_ended` or `call_analyzed` events?
* Why is my Retell webhook signature verification failing?
* How do I handle transcript, transfer, and chat events from Retell?

## Verification (core)

Retell signs each webhook with HMAC-SHA256 using your Retell API key as
the secret (only an API key with the webhook badge in the dashboard works). The
signature arrives in the `X-Retell-Signature` header formatted as
`v={unix_ms_timestamp},d={hex_digest}`, where the digest is computed over the
raw request body concatenated with the timestamp. Always verify against the
raw body, never a re-serialized JSON string.

The Python SDK ships a verify helper (`client.verify(body, api_key, signature)` —
positional params, so the keyword form used in the FastAPI example also works).
The Node SDK has no verify helper, so Node handlers verify manually.

> Verified against `retell-sdk` 5.56.0 (PyPI) and 5.46.0 (npm): the Python
> package exposes `retell.lib.webhook_auth.verify`, re-exported as `client.verify`;
> the npm package has no webhook/verify export. Check your installed version — the
> helper's presence and argument order have moved between releases.

```javascript
const crypto = require('crypto');

// Reject signatures older than 5 minutes to prevent replay attacks
const FIVE_MINUTES_MS = 5 * 60 * 1000;

function verifyRetellSignature(rawBody, signatureHeader, apiKey) {
  const match = /^v=(\d+),d=(.*)$/.exec(signatureHeader || '');
  if (!match) return false;
  const [, timestamp, digest] = match;
  if (Math.abs(Date.now() - Number(timestamp)) > FIVE_MINUTES_MS) return false;

  const expected = crypto
    .createHmac('sha256', apiKey)
    .update(rawBody + timestamp) // raw body + timestamp, in that order
    .digest('hex');
  try {
    return crypto.timingSafeEqual(Buffer.from(expected), Buffer.from(digest));
  } catch {
    return false; // length mismatch = invalid
  }
}

```

Python (FastAPI) uses the official SDK instead:

```python
from retell import Retell

client = Retell(api_key=os.environ["RETELL_API_KEY"])
# client.verify enforces the ~5 min timestamp window and returns a bool
is_valid = client.verify(raw_body.decode("utf-8"),
                         api_key=os.environ["RETELL_API_KEY"],
                         signature=signature_header)

```

> For complete handlers with tests, see [examples/express/](https://github.com/hookdeck/webhook-skills/tree/main/skills/retell-webhooks/examples/express/), [examples/nextjs/](https://github.com/hookdeck/webhook-skills/tree/main/skills/retell-webhooks/examples/nextjs/), [examples/fastapi/](https://github.com/hookdeck/webhook-skills/tree/main/skills/retell-webhooks/examples/fastapi/).

## Common Event Types

| Event | Triggered When | Common Use Cases |
| --- | --- | --- |
| `call_started` | A call begins | Track live calls, update dashboards |
| `call_ended` | A call finishes (audio done) | Persist call record, trigger follow-ups |
| `call_analyzed` | Post-call analysis completes | Store transcript, sentiment, summary |
| `transcript_updated` | Transcript changes mid-call | Live captions, real-time monitoring |
| `transfer_started` | An agent transfer begins | Log routing, notify agents |
| `transfer_bridged` | Transfer connected | Update call state |
| `transfer_cancelled` | Transfer cancelled | Revert routing state |
| `transfer_ended` | Transfer completed | Reconcile call legs |
| `chat_started` | A chat session begins | Track chat sessions |
| `chat_ended` | A chat session ends | Persist chat record |
| `chat_analyzed` | Post-chat analysis completes | Store chat summary, sentiment |

Payloads carry an `event` field plus a `call` object (voice/transfer events) or a
`chat` object (chat events). Dedupe on `event` + `call.call_id` (or `chat.chat_id`) —
Retell retries up to 3 times if it doesn't get a 2xx within 10 seconds.

See [references/overview.md](https://github.com/hookdeck/webhook-skills/blob/main/skills/retell-webhooks/references/overview.md) for full payload structure.

## Environment Variables

```bash
# The Retell API key (must have the webhook badge). Used as the HMAC secret.
RETELL_API_KEY=key_xxxxxxxxxxxxxxxxxxxxxxxx
PORT=3000

```

## Local Development

For local webhook testing, run the Hookdeck CLI via `npx` — no install required:

```bash
npx hookdeck-cli listen 3000 retell --path /webhooks/retell

```

No account required — the CLI creates a guest account on first run and provides a
local tunnel + web UI for inspecting requests.

## Resources

* [Overview](https://github.com/hookdeck/webhook-skills/blob/main/skills/retell-webhooks/references/overview.md) - What Retell webhooks are, event types, payloads
* [Setup](https://github.com/hookdeck/webhook-skills/blob/main/skills/retell-webhooks/references/setup.md) - Configure account-level and agent-level webhooks
* [Verification](https://github.com/hookdeck/webhook-skills/blob/main/skills/retell-webhooks/references/verification.md) - Signature verification details and gotchas
* [Express Example](https://github.com/hookdeck/webhook-skills/tree/main/skills/retell-webhooks/examples/express/) - Complete Express.js implementation
* [Next.js Example](https://github.com/hookdeck/webhook-skills/tree/main/skills/retell-webhooks/examples/nextjs/) - Next.js App Router implementation
* [FastAPI Example](https://github.com/hookdeck/webhook-skills/tree/main/skills/retell-webhooks/examples/fastapi/) - Python FastAPI implementation (uses the Retell SDK)