the-algorithm/RETREIVAL_SIGNALS.md

Signals for Candidate Sources

Overview

The candidate sourcing stage within the Twitter Recommendation algorithm serves to significantly narrow down the item size from approximately 1 billion to just a few thousand. This process utilizes Twitter user behavior as the primary input for the algorithm. This document comprehensively enumerates all the signals during the candidate sourcing phase.

Signals	Description
Author Follow	The accounts which user explicit follows.
Author Unfollow	The accounts which user recently unfollows.
Author Mute	The accounts which user have muted.
Author Block	The accounts which user have blocked
Tweet Favorite	The tweets which user clicked the like botton.
Tweet Unfavorite	The tweets which user clicked the unlike botton.
Retweet	The tweets which user retweeted
Quote Tweet	The tweets which user retweeted with comments.
Tweet Reply	The tweets which user replied.
Tweet Share	The tweets which user clicked the share botton.
Tweet Bookmark	The tweets which user clicked the bookmark botton.
Tweet Click	The tweets which user clicked and viewed the tweet detail page.
Tweet Video Watch	The video tweets which user watched certain seconds or percentage.
Tweet Don't like	The tweets which user clicked "Not interested in this tweet" botton.
Tweet Report	The tweets which user clicked "Report Tweet" botton.
Notification Open	The push notification tweets which user opened.
Ntab click	The tweets which user click on the Notifications page.
User AddressBook	The author accounts identifiers of the user's addressbook.

Usage Details

Twitter uses these user signals as training labels and/or ML features in the each candidate sourcing algorithms. The following tables shows how they are used in the each components.

Signals	USS	SimClusters	TwHin	UTEG	FRS	Light Ranking
Author Follow	Features	Features / Labels	Features / Labels	Features	Features / Labels	N/A
Author Unfollow	Features	N/A	N/A	N/A	N/A	N/A
Author Mute	Features	N/A	N/A	N/A	Features	N/A
Author Block	Features	N/A	N/A	N/A	Features	N/A
Tweet Favorite	Features	Features	Features / Labels	Features	Features / Labels	Features / Labels
Tweet Unfavorite	Features	Features	N/A	N/A	N/A	N/A
Retweet	Features	N/A	Features / Labels	Features	Features / Labels	Features / Labels
Quote Tweet	Features	N/A	Features / Labels	Features	Features / Labels	Features / Labels
Tweet Reply	Features	N/A	Features	Features	Features / Labels	Features
Tweet Share	Features	N/A	N/A	N/A	Features	N/A
Tweet Bookmark	Features	N/A	N/A	N/A	N/A	N/A
Tweet Click	Features	N/A	N/A	N/A	Features	Labels
Tweet Video Watch	Features	Features	N/A	N/A	N/A	Labels
Tweet Don't like	Features	N/A	N/A	N/A	N/A	N/A
Tweet Report	Features	N/A	N/A	N/A	N/A	N/A
Notification Open	Features	Features	Features	N/A	Features	N/A
Ntab click	Features	Features	Features	N/A	Features	N/A
User AddressBook	N/A	N/A	N/A	N/A	Features	N/A