CrowdTangle is a tool that allows publishers to follow public social media content. One of the things people do is post links in social media posts. Often, those links are short links, like https://fb.me/crowdtanglebot.
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Our CrowdTangle Bot has the job of following links to see if they redirect to a final URL, at which point we stop.
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If you found our CrowdTangle user agent accessing your servers, it's because someone put a link to you on social media, and we're checking to see if it redirects anywhere else. Once we get that answer, we're done.

If you have any further questions, you are welcome to contact us at support@crowdtangle.com.