The Facebook Crawler

The Facebook Crawler crawls the HTML of an app or website that was shared on Facebook via copying and pasting the link or by a Facebook social plugin. The crawler gathers, caches, and displays information about the app or website such as its title, description, and thumbnail image.

Crawler Requirements

  • Your server must use gzip and deflate encodings.
  • Any Open Graph properties need to be listed before the first 1 MB of your website or app, or it will be cutoff.
  • Ensure that the content can be crawled by the crawler within a few seconds or Facebook will be unable to display the content.
  • Your app or website should either generate and return a response with all required properties according to the bytes specified in the Range header of the crawler request or it should ignore the Range header altogether.
  • Allowlist either the user agent strings or the IP addresses (more secure) used by the crawler.
  • Ensure that your app or website allows the Facebook Crawler to crawl the privacy policy associated with your app or website.

Crawler IPs and User Agents

The Facebook crawler user agent strings:

  • facebookexternalhit/1.1 (+http://www.facebook.com/externalhit_uatext.php)
  • facebookexternalhit/1.1

To get a current list of IP addresses the crawler uses, run the following command.

whois -h whois.radb.net -- '-i origin AS32934' | grep ^route  

These IP addresses change often.

Example Response

...
route:      69.63.176.0/21
route:      69.63.184.0/21
route:      66.220.144.0/20
route:      69.63.176.0/20
route6:     2620:0:1c00::/40
route6:     2a03:2880::/32
route6:     2a03:2880:fffe::/48
route6:     2a03:2880:ffff::/48
route6:     2620:0:1cff::/48
... 

Troubleshooting

If your app or website content is not available at the time of crawling, you can force a crawl once it becomes available either by passing the URL through the Sharing Debugger tool or by using the Sharing API.

You can simulate a crawler request with the following code:

curl -v --compressed -H "Range: bytes=0-524288" -H "Connection: close" -A "facebookexternalhit/1.1 (+http://www.facebook.com/externalhit_uatext.php)" "$URL"