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This really puzzles me. Many of us know that now with Facebook API v2 you can only get the mutual friends who also gave permission to use your app and have made their list of friends public.

Nevertheless, Tinder manages to show not only all (or most) of your mutual friends (not only Tinder mutual friends), but also show 2nd degree connections.

How in the world do the do this!? IF it is somehow hacking their way, is Facebook OK with this?

cduguet
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My best guess is that Tinder itself maintains list of friends to find mutual friends.

FB can return a list of friends that also use your app.

Given users A, B, C with your app installed:

Given A is friends with B and B is friends with C.

You can infer for user A and C that there is a mutual friend B.

Harry Moreno
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Zaki Anwar Hamdani
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  • Then, there might be something pointing to that in their Privacy Policy. I might take a look at it later. Also, since they cannot get friends' IDs anymore (Facebook user ID, not app-scoped ID), this might only work with users who subscribed before they made the transition to API v2 – cduguet Aug 13 '15 at 01:34
  • @cduguet: Why would it matter whether the user id was app-scoped or not? – CBroe Aug 13 '15 at 09:59
  • You are right it doesn't matter, I thought these app-scoped ID's also change between requests. I'm still not sure about it though. – cduguet Aug 13 '15 at 21:04
  • How would Tinder keep lists of friends, when FB no longer provides these? – Gregory Magarshak Dec 24 '17 at 17:34
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Tinder most likely gets this information using the All Mutual Friends API:

https://developers.facebook.com/docs/graph-api/reference/user-context/all_mutual_friends

Gregory Magarshak
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  • link is broken and that api is deprecated for Graph API v3.1 on July 26, 2018, and will be deprecated for all versions on October 24, 2018. https://developers.facebook.com/docs/apps/review/feature#reference-ALL_MUTUAL_FRIENDS – Harry Moreno Sep 11 '18 at 19:45