Combat

Every roll happens on the server. The client only sends “I want to attack this monster”; the server decides what happened.

Hit resolution

Attacks roll a d20:

d20 + attack bonus >  target Guard   →  hit
d20 + attack bonus ≤  target Guard   →  miss

Note it’s strictly greater. Rolling exactly the target’s Guard is a miss.

Attack bonus:

Base = floor(level / 2)
Player melee adds your STR modifier
Monsters use their data value if they have one, otherwise the level default

Hit chance

Columns are the target’s Guard, rows are your total attack bonus.

Attack bonus	Guard 8	Guard 9	Guard 10	Guard 11	Guard 13	Guard 15
+0	60%	55%	50%	45%	35%	25%
+1	65%	60%	55%	50%	40%	30%
+2	70%	65%	60%	55%	45%	35%
+3	75%	70%	65%	60%	50%	40%
+4	80%	75%	70%	65%	55%	45%
+5	85%	80%	75%	70%	60%	50%
+6	90%	85%	80%	75%	65%	55%
+7	95%	90%	85%	80%	70%	60%
+8	100%	95%	90%	85%	75%	65%
+9	100%	100%	95%	90%	80%	70%
+10	100%	100%	100%	95%	85%	75%

Hitting each monster

Look up your total attack bonus (half your level, plus your STR modifier):

Monster	Guard	+0	+2	+4	+6	+8
Kobold	8	60%	70%	80%	90%	100%
Goblin	9	55%	65%	75%	85%	95%
Stalker	10	50%	60%	70%	80%	90%
Female Orc	10	50%	60%	70%	80%	90%
Orc	11	45%	55%	65%	75%	85%
Goblin Chief	11	45%	55%	65%	75%	85%
Orc Warlord	13	35%	45%	55%	65%	75%

Monsters hitting you

The other direction, by your Guard (DEX base plus equipment):

Monster	To-hit	Your Guard 10	Your Guard 14	Your Guard 18	Your Guard 22	Damage on hit
Kobold	+0	50%	30%	10%	0%	1d4
Goblin	+1	55%	35%	15%	0%	1d4
Stalker	+1	55%	35%	15%	0%	1d6
Orc	+2	60%	40%	20%	0%	1d6
Female Orc	+3	65%	45%	25%	5%	1d6
Goblin Chief	+2	60%	40%	20%	0%	1d8
Orc Warlord	+6	80%	60%	40%	20%	2d8

Stacking Guard pays off very directly — each +1 costs the attacker 5% hit chance. A full plate set (19 Guard total) makes you nearly unhittable by low-level monsters.

Damage

Damage is only rolled on a hit. Dice notation is {count}d{sides}:

2d6  →  roll two six-sided dice and sum (2–12)

Player melee adds your STR modifier.

Weapon damage

Weapon	Damage	Min	Avg	Max	Weight
Iron Sword	1d8	1	4.5	8	3 kg
Worn Iron Sword	1d6	1	3.5	6	3 kg
Spear	1d6	1	3.5	6	4 kg
Dagger	1d4	1	2.5	4	1 kg
Goblin Sword	1d4	1	2.5	4	2 kg
Small Sword	1d4	1	2.5	4	1.5 kg
Torch	1d4	1	2.5	4	1 kg
Worn Torch	1d4	1	2.5	4	1 kg

The STR modifier applies to every hit, so it lifts low-damage weapons proportionally more: STR 18 (+4) with a Dagger (1d4, average 2.5) actually averages 6.5 — 2.6× the base.

The Guard scale

Guard is NetHack’s AC inverted — higher is better.

Guard	Meaning
0–7	Barely defended
8–9	Light defence
10	Ordinary
11–13	Solid
14+	Heavy armor and up

Against NetHack: Guard = 10 − AC.

Experience

XP per kill

XP = 1 + level² + max(Guard - 10, 0) × 2

Guard above 10 earns a bonus — harder monsters pay more.

Monster	Level	Guard	XP	Health	XP / health
Kobold	1	8	2	5	0.40
Goblin	2	9	5	9	0.56
Stalker	3	10	10	14	0.71
Female Orc	4	10	17	18	0.94
Orc	4	11	19	18	1.06
Goblin Chief	5	11	28	23	1.22
Orc Warlord	10	13	107	120	0.89

XP / health is the efficiency column — higher means more XP per point of health you have to chew through. The Orc Warlord gives the most XP but takes 120 health to get there, so it isn’t the most efficient.

XP to level

XP(n) = 20 × 2^(n-2)      (n ≥ 2)

Every level costs exactly twice the last — a pure exponential with no easing.

Level	Cumulative XP	This level costs	Orcs, roughly
1	0	—	—
2	20	20	2
3	40	20	2
4	80	40	3
5	160	80	5
6	320	160	9
7	640	320	17
8	1,280	640	34
9	2,560	1,280	68
10	5,120	2,560	135
11	10,240	5,120	270
12	20,480	10,240	539
13	40,960	20,480	1,078
14	81,920	40,960	2,156
15	163,840	81,920	4,312
16	327,680	163,840	8,624
17	655,360	327,680	17,247
18	1,310,720	655,360	34,493
19	2,621,440	1,310,720	68,986
20	5,242,880	2,621,440	137,971

The last column converts to Orcs (level 4, Guard 11, 19 XP each). Past the first ten levels, grinding on the current monster roster gets very slow — the game’s content today lines up with roughly the first ten levels.

The death penalty

Dying costs no equipment but does cost XP:

level band = XP(L+1) - XP(L)
penalty    = max(1, floor(band × 0.15))

That’s 15% of your progress through the current level.

Losing a level

If the deduction drops you below the level’s starting XP you lose a level. Two protections:

At most one level per death.
Level 1 never drops.

After a drop your XP is floored at 30% through the lower band, so you don’t end up stuck just short of relevelling over and over.

Level	Level band	Lost on death	Orcs to recover
2	20	3	1
3	40	6	1
4	80	12	1
5	160	24	2
6	320	48	3
7	640	96	6
8	1,280	192	11
9	2,560	384	21
10	5,120	768	41
11	10,240	1,536	81
12	20,480	3,072	162
13	40,960	6,144	324

Losing a level costs health too

So that repeatedly levelling up and down can’t be farmed for health, the distribution of health lost on a level-down is identical to the health gained on a level-up:

roll the hit die, guarantee at least half, add the CON modifier

The long-run expectation is therefore zero — no statistical gain from cycling. Health also never drops below your level 1 value.

Hit die	Classes	Expected gain / loss
d10	Barbarian, Caveman, Knight, Valkyrie	6.50
d8	Ranger, Samurai, Monk, Priest	5.25
d6	Archaeologist, Healer, Rogue, Wizard	4.00
d4	Tourist	2.75

If you didn’t lose a level, you don’t lose health.

Respawning

Request a respawn and the server confirms your health is 0, refills it and returns you to the origin (0, 0, 0). Satiation resets to 300 — the bottom of the Well-Fed band — so you don’t respawn starving and immediately go Weak.

Monster AI

Monster AI runs on the client, but attack resolution always goes to the server.

State	Meaning
`idle`	Waiting (30% chance to wander)
`walk`	Moving
`run`	Chasing a player (within chase range)
`attack`	Attacking (within attack range)
`hit`	Stagger from being hit (~800 ms)
`dead`	Dead

A dead monster is removed after 30 seconds. Per-monster chase ranges and attack intervals are in Monster index.