retell-webhooks

# 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/](examples/express/), [examples/nextjs/](examples/nextjs/), [examples/fastapi/](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](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](references/overview.md) - What Retell webhooks are, event types, payloads - [Setup](references/setup.md) - Configure account-level and agent-level webhooks - [Verification](references/verification.md) - Signature verification details and gotchas - [Express Example](examples/express/) - Complete Express.js implementation - [Next.js Example](examples/nextjs/) - Next.js App Router implementation - [FastAPI Example](examples/fastapi/) - Python FastAPI implementation (uses the Retell SDK) ## Recommended: webhook-handler-patterns We recommend installing the [webhook-handler-patterns](https://github.com/hookdeck/webhook-skills/tree/main/skills/webhook-handler-patterns) skill alongside this one for handler sequence, idempotency, error handling, and retry logic. Key references (open on GitHub): - [Handler sequence](https://github.com/hookdeck/webhook-skills/blob/main/skills/webhook-handler-patterns/references/handler-sequence.md) — Verify first, parse second, handle idempotently third - [Idempotency](https://github.com/hookdeck/webhook-skills/blob/main/skills/webhook-handler-patterns/references/idempotency.md) — Dedupe Retell retries on `event` + `call_id` - [Error handling](https://github.com/hookdeck/webhook-skills/blob/main/skills/webhook-handler-patterns/references/error-handling.md) — Return codes, logging, dead letter queues - [Retry logic](https://github.com/hookdeck/webhook-skills/blob/main/skills/webhook-handler-patterns/references/retry-logic.md) — Provider retry schedules, backoff patterns ## Related Skills - [elevenlabs-webhooks](https://github.com/hookdeck/webhook-skills/tree/main/skills/elevenlabs-webhooks) - ElevenLabs voice AI webhook handling - [deepgram-webhooks](https://github.com/hookdeck/webhook-skills/tree/main/skills/deepgram-webhooks) - Deepgram transcription callback handling - [openai-webhooks](https://github.com/hookdeck/webhook-skills/tree/main/skills/openai-webhooks) - OpenAI webhook handling - [twilio-webhooks](https://github.com/hookdeck/webhook-skills/tree/main/skills/twilio-webhooks) - Twilio voice and messaging webhook handling - [stripe-webhooks](https://github.com/hookdeck/webhook-skills/tree/main/skills/stripe-webhooks) - Stripe payment webhook handling - [github-webhooks](https://github.com/hookdeck/webhook-skills/tree/main/skills/github-webhooks) - GitHub repository webhook handling - [webhook-handler-patterns](https://github.com/hookdeck/webhook-skills/tree/main/skills/webhook-handler-patterns) - Handler sequence, idempotency, error handling, retry logic - [hookdeck-event-gateway](https://github.com/hookdeck/webhook-skills/tree/main/skills/hookdeck-event-gateway) - Webhook infrastructure that replaces your queue — guaranteed delivery, automatic retries, replay, rate limiting, and observability for your webhook handlers