I'm more of a builder than a player I got into D&D tooling because the encounter math always looked like the most fixable problem. The DMG XP thresholds, the monster count multiplier, the back-and-forth... it felt like something a calculator should just handle.
So I built EncounterForge 5e.
Free, no account needed:
Real-time difficulty rating (Easy / Medium / Hard / Deadly) with full XP breakdown
168 SRD monsters, filterable by CR, type, HP, AC
Auto-Suggest picks monster combos to hit a target difficulty for your specific party (3x/day)