From publisher blurb:
Old-School Essentials is an adventure role-playing game of exploration, danger, monsters, and magic. The game is intentionally rules-light, putting the focus of play on imagination, improvisation, and fun. The rules are optimised for ease of use at the table, with meticulous attention to wording and layout clarity. What's more, Old-School Essentials is 100% compatible with the classic Basic/Expert game from 1981, meaning that decades of adventure are at your fingertips!
The Basic Rules
This book is an art-free sample of the basic rules of the game required by players:
The full introduction and character creation rules.
The four core human classes: cleric, fighter, magic-user, thief.
Full lists of adventuring equipment, weapons, and armour.
The rules for dungeon adventures, encounters, and combat.
The full rules for spell casting, and the list of 1st level spells.