Agent skill

Smartcar Webhooks Skill

Receive and verify Smartcar webhooks. Use when setting up Smartcar webhook handlers, debugging SC-Signature verification, responding to the VERIFY challenge, or handling vehicle events like VEHICLE_STATE and VEHICLE_ERROR.

Install this skill

npx skills add hookdeck/webhook-skills --skill smartcar-webhooks

When to Use This Skill

How do I receive Smartcar webhooks?
How do I verify the Smartcar SC-Signature header?
How do I respond to the Smartcar VERIFY challenge so my webhook activates?
How do I handle VEHICLE_STATE and VEHICLE_ERROR events?
Why is my Smartcar webhook signature verification failing?

Verification (core)

Smartcar signs every webhook with a hex-encoded HMAC-SHA256 of the raw request body, keyed with your Application Management Token (AMT, from the Smartcar Dashboard), in the SC-Signature header. On setup Smartcar also POSTs a one-time VERIFY event whose data.challenge you must hash with the same AMT and echo back within 15 seconds — otherwise the webhook never activates. This is Smartcar's own scheme, not the Standard Webhooks spec.

The official SDKs expose two helpers: hashChallenge/hash_challenge (hex HMAC of any string) and verifyPayload/verify_payload (compares the header against the body's HMAC).

Node (Express, Next.js):

const smartcar = require('smartcar');
const AMT = process.env.SMARTCAR_MANAGEMENT_TOKEN;

// 1. VERIFY handshake — echo the hashed challenge so the webhook activates
if (event.eventType === 'VERIFY') {
  const hmac = smartcar.hashChallenge(AMT, event.data.challenge); // hex string
  return res.status(200).json({ challenge: hmac });
}

// 2. Data events — verify SC-Signature (hex HMAC-SHA256 of the raw body).
//    The Node SDK re-serializes the parsed body internally, so pass the object.
if (!smartcar.verifyPayload(AMT, req.headers['sc-signature'], event)) {
  return res.status(401).send('Invalid signature');
}

Python (FastAPI) — the SDK hashes the raw body string you pass in:

import smartcar
amt = os.environ["SMARTCAR_MANAGEMENT_TOKEN"]

if event["eventType"] == "VERIFY":
    return {"challenge": smartcar.hash_challenge(amt, event["data"]["challenge"])}

if not smartcar.verify_payload(amt, request.headers["sc-signature"], raw_body):
    raise HTTPException(status_code=401, detail="Invalid signature")

For complete handlers with route wiring, VERIFY handling, event dispatch, and tests, see:
examples/express/
examples/nextjs/
examples/fastapi/

Common Event Types

`eventType`	Triggered When	Common Use Cases
`VERIFY`	Webhook is created or re-verified from the Dashboard	Echo the hashed `data.challenge` to activate the webhook
`VEHICLE_STATE`	A monitored signal changes (e.g. battery state of charge, odometer)	Sync vehicle data, trigger alerts, update dashboards
`VEHICLE_ERROR`	Smartcar fails to retrieve a subscribed signal	Surface connection issues; a follow-up event with `state: "RESOLVED"` fires on recovery

Legacy v2 scheduled / eventBased webhooks are deprecated — use the event types above.

For the full event reference, see Smartcar Webhook Events.

Environment Variables

SMARTCAR_MANAGEMENT_TOKEN=xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx  # Application Management Token from the Dashboard

The Application Management Token is the only secret needed to verify payloads and answer the VERIFY challenge — it keys every HMAC.

Local Development

# Start tunnel (no account needed)
npx hookdeck-cli listen 3000 smartcar --path /webhooks/smartcar

Reference Materials

references/overview.md - Smartcar webhook concepts, event types, payload structure
references/setup.md - Dashboard configuration, Application Management Token, subscribing vehicles
references/verification.md - SC-Signature verification, VERIFY challenge, manual HMAC, gotchas