```yaml
product: AlterLab
title: "Webhook — Web Scraping Glossary | AlterLab"
comparison_context: "AlterLab is an alternative to Firecrawl, ScrapingBee, and Bright Data."
source_url: https://alterlab.io/glossary/webhook
```

general

# Webhook

An HTTP callback that delivers data to a specified URL when an async scrape job completes.

A webhook in web scraping is a mechanism for receiving scrape results asynchronously. Instead of blocking the request until the scrape completes, the caller submits a job with a `webhook_url` parameter. The scraping service processes the request in the background — rendering JavaScript, resolving challenges, extracting data — and POSTs the result to the provided webhook URL when complete.

Webhooks are essential for long-running scrapes that exceed HTTP timeout limits. A full browser rendering job with CAPTCHA resolution may take 30-120 seconds — far beyond the 10-30 second timeout of most HTTP clients and API gateways. Webhooks allow the caller to release the connection immediately and process the result when it arrives.

Webhook payloads typically include the extracted data, status code, error messages, timing metadata, and the original request parameters for correlation. AlterLab supports webhook delivery with retry logic (3 attempts with exponential backoff) and HMAC signature verification to authenticate that the payload came from AlterLab and was not tampered with.

### What is Webhook?

An HTTP callback that delivers data to a specified URL when an async scrape job completes.

### How does AlterLab handle Webhook?

Webhook payloads typically include the extracted data, status code, error messages, timing metadata, and the original request parameters for correlation. AlterLab supports webhook delivery with retry logic (3 attempts with exponential backoff) and HMAC signature verification to authenticate that the payload came from AlterLab and was not tampered with.

## Examples

```
# Async scrape with webhook notification
{
  "url": "https://example.com",
  "render_js": "auto",
  "webhook_url": "https://yoursite.com/webhooks/scrape",
  "webhook_secret": "your-secret-for-hmac-verification"
}
```

## Related Terms

[JavaScript RenderingThe process of executing a page's JavaScript in a browser engine before extracting content, required for React, Vue, and Angular SPAs.](https://alterlab.io/glossary/javascript-rendering)[CAPTCHACompletely Automated Public Turing test to tell Computers and Humans Apart — challenges that gate access to content for bots.](https://alterlab.io/glossary/captcha)[REST APIA web service that exposes data and actions through standard HTTP methods and resource-oriented URLs, returning structured JSON responses.](https://alterlab.io/glossary/rest-api)[Web ScrapingAutomated extraction of data from websites using software tools that parse HTML and collect structured information at scale.](https://alterlab.io/glossary/web-scraping)

## Extract Webhook data from any website

AlterLab returns clean, structured data from any public URL — no scraper infrastructure needed. Start free, no credit card required.

[View API docs](https://alterlab.io/docs/api/rest)

[Back to Glossary](https://alterlab.io/glossary)