Sleeper is a free, mobile-first fantasy sports platform best known for its fantasy football leagues, highly customizable settings, and in-app chat that keeps a league’s trash talk and transactions in one place. Beyond season-long leagues it also runs standalone games like NFL pick’em, survivor, and mock drafts.

Its appeal to commissioners is flexibility: scoring, roster, waiver, taxi, and format options are deep enough to support redraft, keeper, dynasty, superflex, and best-ball leagues without leaving the app. That same depth is why Sleeper has become the default home for engaged and dynasty players.

Where Sleeper stops is the league’s longer memory and its off-platform side games. It runs each season as its own object and keeps its native pick’em and survivor games over NFL results rather than over your league’s own matchups. LeagueSide connects to a Sleeper league read-only — no password stored — and layers on multi-season records, standings, and league-native Pick’em and Survivor. Sleeper is fully supported today; ESPN and Yahoo are planned for the 2026 season.