Encounter Lab
D&D 2024 SRD · Monte-Carlo

Stop guessing if an encounter is balanced.
Run it 100 times instead.

Encounter Lab actually simulates combat — multiattack, legendary actions, concentration breaks, opportunity attacks, the whole action economy — then tells you the real party win rate.

300+
SRD monsters
100s
Battles per second
2024
PHB rules

Built for actual prep

Every tactical detail the books care about, modeled in code.

Real combat sim

Multiattack, legendary actions, recharge abilities, AoE geometry, concentration saves, opportunity attacks, death saves. Not XP-budget math.

Party preset or custom

Standard 5-PC adventuring party, or roll your own with point buy / heroic arrays. Class loadouts include the spells they'd actually prepare.

SRD monster roster

Every 2024 SRD creature with tactics, recharge timing, and legendary action priorities derived from the stat block.

Build custom monsters

Full editor for traits, actions, bonus actions, reactions, legendary actions, and spellcasting. Saved to your account.

Battle Replay

Watch any saved battle play out round-by-round on a tactical map, or step through it event-by-event with action bubbles.

Honest results

Win rate, average rounds, survivors, casualties — aggregated across 100+ runs so one freak crit doesn't fool you.

Why not just use a CR calculator?

Because XP-budget math doesn't model the fight.

What everyone else does vs. what Encounter Lab does

XP-budget calculators

  • Look at monster CR vs. party level
  • Multiply by an encounter-difficulty fudge factor
  • Spit out "Hard" or "Deadly"
  • Never actually run the fight
  • Wildly miss on solo bosses, casters, action-economy disparities

Encounter Lab

  • Builds a real battlefield with positions
  • Picks tactics for each monster every round
  • Resolves attacks, saves, damage, conditions
  • Tracks concentration, spell slots, recharges, legendary pools
  • Reports the actual win rate — not a label

Ready to stop second-guessing the fight?

Sign in with your DM's Toolkit / RealmEngine account — no separate signup needed.

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