Racial Stealth Modifier

Every race has a racial stealth modifier associated with it. From the in-game help for Racial Stealth:

Stealth is two-fold: A stealthy race is less likely to be attacked by aggressive mobs when a less-stealthy target also presents itself.

A stealthy race will also succeed more often with rogue skills such as blackjack, backstab and sneak attack.

Some examples of stealthy races include Drow, Halfling and Demonseed.

Some examples of non-stealthy races include Giant, Troglodyte and Troll.

Because we can't be sure exactly what the number is, we have simply assigned each race a rating of -3 to 2, with negative numbers being a penalty, 0 meaning "no modifier", and 2 being the best modifier possible. -3 is a failure rate of approximately 50%, -2 is 20%, and -1 is 5%. Note that size and groupsize both affect the success rate of disengage and slip, and are separate from the inherent stealth modifier.

There is also a separate archery damage modifier and melee damage modifier for each race.

Please note that all of this information has been gleaned from race pages here as well as discussion in-game, and is subject to change at any time. Also, entries for evolution races should reflect their maximum (highest evolve).

Legend
Great	2
Good	1
Average	0
Below Average	-1
Bad	-2
Terrible	-3

Creatable Races Stealth Modifiers

Race	Size	Racial Stealth Modifier
Centaur	L	-1
Deep Gnome	S	1
Draconian	M	-2
Drow	M	2
Duergar	S	0
Dwarf	S	-1
Elf	M	1
Ent	vL	-3
Firedrake	vS-vL	-3
Gargoyle	M	-1
Giant	vL	-1
Gnome	S	1
Goblin	S	1
Halfling	S	2
Half-Elf	M	1
Half-Orc	M	0
Harpy	M	1
Human	M	0
Imp	vS-vL	-2 to 1
Kobold	S	2
Kzinti	M	1
Lizardmen	M	-1
Ogres	L	-2
Orc	M	-1
Troglodyte	M	-2

Remort Races Stealth Modifiers

Race	Size	Racial Stealth Modifier
Demonseed	S	2
Dragon	vL	-2
Golem	L	-3
Griffon	L	0
High Elf	M	1
Hobgoblin	S	1
Minotaur	L	-1
Miraar	M	0
Sprite	vS	0
Troll	L	-1
Tuataur	M	1

Stealth Modifiers, Rogue Skills, And You

Performance as a rogue is not exclusively or even primarily determined by the stealth modifier. Dexterity, racial damage modifier and size also affect rogue skills to varying degrees but these are separate from the hidden natural stealth modifier as described above. Many players strongly prefer sturdy races with high damage output to small agile races when they create a rogue, as rogues have difficulty avoiding taking damage in the course of their duties.

Most races do not have a stealth modifier. The stealth modifier is most plainly obvious when using backstab, as when it is rolled you get the message "it sees you coming from a mile away" and your backstab fails completely. From this you can clearly see some things - trolls have a -5% modifier, dragons are -20%. However, it doesn't measure positive stealth modifier in any way, and these positive stealth modifiers are extremely rare... most races which are considered "stealthy" are just neutral with above average intelligence/dex, which is sufficient to succeed on backstab all the time.

Other skills fail for other reasons - most importantly, slip and disengage are strongly affected by size and groupsize, as your ability to disappear in a crowd is considered extremely important there. "Nils" on assassinate and backstab occur at a flat rate regardless of race or class. From this we can see differences in orc and troll stealth performance, despite them having the same negative modifier - orcs have more dex, and also are medium instead of large, so they stab slightly better and slip significantly better.

Nil damage is not a failure due to stealth. Only failure which result in a mob turning to face you, or see you coming a mile away counts as a failure to be sneaky.