mibextid?Tokens Facebook's mobile apps attach to links you share out of them, recording the share context so opens can be traced back to it.
This page covers both mobile share tokens: mibextid and sfnsn.
Share a post from the Facebook or Messenger mobile app and the link arrives carrying mibextid (the name suggests Meta in-app browser external ID) and often sfnsn, whose values differ by share channel: copy link, WhatsApp share, SMS share and so on each stamp their own.
Together they tell Meta how the link left the app and let opens be attributed back to the share event. They started appearing around 2022 as Meta rebuilt its share links, and they follow the link into every chat and inbox it gets pasted into.
Yes. The Facebook post or page loads identically without them. They only feed Meta's share attribution.
Rather's Link Shortener strips mibextid and hundreds of parameters like it, right in the address bar and in everything you copy or share. Free, open source, no account, no data collection, and the page you are on never breaks: the cleanup happens after the site has already loaded.