The Game Master Companion 5e is a mobile-friendly tool that lets GMs handle quickly and comprehensively common rules-complex situations in D&D, such as combat, searching for secret doors, and disabling traps. The core rules of Wizards of the Coast's System Reference Document 5.1 (SRD5) are reorganized by task. The SRD5 consists of essential provisions of the PHB, the DMG, and the MM, and is open game content intended for use by game developers pursuant to the Open Gaming License. Users of the GM Companion 5e are sometimes directed to official sourcebooks for more information.
PHB = Players Handbook
DMG = Dungeon Master's Guide
MM = Monster Manual
XGtE = Xanathar's Guide to Everything
TCoE = Tasha's Cauldron of Everything
SAC = Sage Advice Compendium
Also, interpretations of Jeremy Crawford (JC) are referenced, and infrequently a rule interpretation, comment, or house rule is offered. Welcome and enjoy.