D&D 5e combat rules in Onyx: initiative, attacks, cover, movement, opportunity attacks and more, from the 2014 and 2024 Player’s Handbooks.
Overview
Onyx collects the rules for running a fight: turn order, attack rolls, damage, cover, movement and the special cases that come up mid-combat. Most come from the two Player’s Handbooks, with a few from the Dungeon Master’s Guide.
When to use it
Look here when a fight stalls on a rules question, such as how cover works or when an opportunity attack triggers.