# What is a webhook?

> A webhook is a message one app sends to another the moment something happens. How Meta lead webhooks work, how Slack webhooks post messages, and webhooks vs polling.
- **Author**: Marxx
- **Published**: 2026-11-07
- **Category**: Lead generation
- **URL**: https://marxx.ai/library-glossary/webhook

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A webhook is a message one app sends to another app the moment something happens, posted to a web address the second app gave it. When a new lead fills your Meta form, a webhook is how your CRM or alert tool hears about it within moments instead of checking every few minutes.

## Doorbell vs letterbox

Polling is walking to the letterbox every 15 minutes to check for a parcel. A webhook is a doorbell: the courier rings once, when the parcel arrives.

| | Webhook | Polling |
|---|---|---|
| Who starts it | The app where the event happened | The app that wants the news |
| How fast | Right after the event | At the next check |
| Example | Meta tells your CRM about a new lead | An automation tool asks Meta for new leads on a timer |

Polling still works and is easy to set up. Zapier's Free plan checks every 15 minutes, and IFTTT's Facebook Lead Ads trigger checks every hour on its Free plan (both checked 6 Nov 2026, [Zapier pricing](https://zapier.com/pricing), [IFTTT plans](https://ifttt.com/plans)).

## How a Meta lead webhook works

Meta's lead webhook does not carry the lead's name or phone number. It carries ids.

1. A person submits your instant form.
2. Meta sends a webhook to your app with the lead's id, plus ids such as the form, Page and ad.
3. Your app uses that lead id to ask Meta for the answers, with permission to read leads.
4. Your app saves the lead, sends an alert or both.

If step 3 fails, for example because access was removed, the doorbell rings but the parcel stays locked. Our [Lead Ads Testing Tool guide](/guides/how-to-use-the-facebook-lead-ads-testing-tool) shows how to check the whole chain with a test lead.

## Slack incoming webhooks

Slack works the other way round. An incoming webhook is a web address Slack gives you. Whatever an app sends to it appears as a message in one channel. Two limits from Slack's docs (checked 6 Nov 2026): a message posted this way cannot be deleted by the webhook, and apps should post no more than one message per second per channel, with short bursts allowed.

So a home-made lead alert often chains two webhooks: Meta to your server, then your server to Slack. Our [Slack lead notifications guide](/guides/how-to-get-facebook-lead-notifications-in-slack) compares this with ready-made tools. We make Marxx, which posts each new Meta lead to the client's Slack channel within moments. See [Marxx in Slack](/features/slack).

## FAQ

### Do I need a developer to use webhooks?

To build your own, usually yes. Automation tools and CRMs set up the webhook for you behind a few buttons.

### Is a webhook safe?

Keep webhook addresses private. Anyone who has a Slack incoming webhook address can post to that channel.

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- [More Lead generation articles](https://marxx.ai/library-glossary/category/lead-generation)
- [All articles](https://marxx.ai/library-glossary)