I was updating an internal tool we use at brin.gr while suddenly I needed a way to find the number of times a specific tweet has been favorited. The Search API results didn't include this information even with include_entities set to true.

I knew there was an API for that since the official web & mobile app are able to show this. So after a little network monitoring I finally found the endpoint:

https://api.twitter.com/i/statuses/[tweet.id]/activity/summary.json
Note: the request must be done via OAuth. Sample payload:

{
   "favoriters":[113682166],
   "favoriters_count":"1",
   "repliers":[],
   "repliers_count":"0",
   "retweeters_count":"1",
   "retweeters":[113682166]
}