Why not just use Slack's built-in options? Even where Calendly offers some form of Slack integration, it's often tied to one account, limited in which events it covers, or more than you need. ZestyGlue is a dedicated, always-on feed of exactly the events you choose, for $9/month instead of a full automation-platform subscription.
What it looks like
ZestyGlue
Calendly — Invitee · Created
A real Calendly event, shown as ZestyGlue formats it for Slack.
Setup — about two minutes
- Create the connector. In ZestyGlue, start a new Calendly → Slack connector. You'll get a unique webhook URL right away.
- Point Calendly at it. Calendly's webhook subscriptions are created via their API (or the Integrations panel on Enterprise plans) — create one pointed at your ZestyGlue webhook URL.
- (Optional) copy the signing key. Calendly returns a signing key when you create the subscription — paste it into ZestyGlue for extra verification, though it isn't required to get started.
- Point Slack at ZestyGlue. Create a Slack app (or reuse one) → Incoming Webhooks → Add New Webhook to Workspace, pick the channel, and copy the URL into ZestyGlue.
Under the hood: Calendly's webhook signing key is only returned once, at the moment you create the webhook subscription via their API — copy it into ZestyGlue immediately, since Calendly won't show it again.
Events you can forward
invitee.created
invitee.canceled
Questions
Is my Calendly Webhook Signing Key safe with ZestyGlue?
It's encrypted at rest with Fernet symmetric encryption before it ever touches disk, it's never logged, and it's never displayed again in the dashboard after you enter it — only a masked placeholder is shown.
Does this notify on cancellations as well as new bookings?
Yes — subscribe to both invitee.created and invitee.canceled if you want to see cancellations alongside new bookings.
Do I need a paid Calendly plan to use webhooks?
Calendly requires at least a paid plan to create webhook subscriptions via their API — the free plan doesn't expose this feature.
Does this need Slack admin approval?
No app installation is required on Slack's side — an Incoming Webhook is just a URL generated once. No OAuth review, no admin approval flow.
What happens if my ZestyGlue subscription lapses?
Events are silently dropped rather than causing errors on Calendly's side — Calendly never sees a failure response, so it won't retry aggressively or flag your webhook as broken. Your dashboard will simply stop showing new events until you resubscribe.