What is Webhook?
Definition: An HTTP callback that sends data from one application to another in real-time when a specific event occurs, enabling instant communication between tools without polling.
Webhooks are the nervous system of a GTM stack. When something happens in Tool A (new lead, deal update, email reply), Tool A sends an HTTP POST request to a URL you specify. Tool B receives that data instantly and acts on it. No polling, no delays, no scheduled syncs.
Example: you set up a webhook in Instantly that fires when a prospect replies. The webhook URL points to an n8n workflow. n8n receives the reply data (contact info, email content, timestamp), runs enrichment, creates a CRM record, and notifies the sales team. The entire chain executes in seconds.
Most modern SaaS tools support outgoing webhooks. HubSpot, Salesforce, Instantly, Smartlead, Slack, Stripe, and dozens more. The receiving end is typically an automation platform (n8n, Make, Zapier) or a custom endpoint you build.
Webhooks fail sometimes. The receiving server is down, the payload format changes, or rate limits kick in. Good webhook implementations include retry logic (try again in 30 seconds, then 2 minutes, then 5 minutes), payload logging (so you can replay missed events), and alerting (Slack notification when a webhook fails 3 times). n8n handles retries natively. Custom endpoints need you to build this yourself.