"Play it out" and the Opening Guide are built from these sources.
From the Lichess opening explorer (Lichess database games), as an offline snapshot.
Computed by Stockfish at a fixed depth, offline.
The written explanation of an opening position comes from Chess Opening Theory on Wikibooks, by its contributors, licensed under CC BY-SA 4.0. The text is shown as published in the revision listed below (retrieved 2026-09-27); theory tables, statistics and reference lists are left out. Each page's authors are listed in its history on Wikibooks.