Stealth

Key Ability: Dex | Trained Only: No | Armor Check Penalty: Yes

You are skilled at avoiding detection, allowing you to slip past foes or strike from an unseen position. This skill covers hiding and moving silently.

In general, the use of this skill requires concealment or cover. In addition, you cannot use this ability against a target that has already noticed you. You are automatically noticed if you make an attack (possible exceptions: sniping (see below) and greater invisibility). If a target has already seen you, you can use stealth only after you have dropped out of line of sight (for example, by going around a corner) or if you create a diversion to hide (see below).

Check: Use this skill to sneak around and remain hidden from others. If you are trying to use stealth around other creatures, your Stealth check is generally opposed by their Spot check, but if they are actively on watch and trying deliberately to be alert, they use their Search check to sense you. A creature larger or smaller than Medium takes a size bonus or penalty on Stealth checks depending on its size category: Fine +16, Diminutive +12, Tiny +8, Small +4, Large -4, Huge -8, Gargantuan -12, Colossal -16.

Moving with Stealth: You can move up to half your normal speed and use Stealth at no penalty. When moving at a speed greater than half and up to your normal speed, you take a -5 penalty. It's practically impossible to use Stealth while running or charging (you take a -20 penalty to try to do so). You cannot use stealth after making an attack. (Exceptions are rare: see Sniping, below, or if you remain unseen after the attack, as against a blinded foe or while using an effect such as Greater Invisibility.)

Breaking Stealth: When you start your turn using Stealth, you can leave cover or concealment and remain unobserved as long as you succeed at a Stealth check and end your turn in cover or concealment. Your Stealth immediately ends after you make an attack roll, whether or not the attack is successful (except when sniping as noted below).

Sniping: If you've already successfully used Stealth at least 10 feet from your target, you can make one ranged attack and then immediately use Stealth again. You take a -20 penalty on your Stealth check to remain hidden.

Creating a Diversion to Hide: You can use Bluff to allow you to use Stealth. A successful Bluff check can give you the momentary diversion you need to attempt a Stealth check while people are aware of you. While the others turn their attention from you, you can attempt a Stealth check if you can get to an unobserved place of some kind. This check, however, is made at a -10 penalty because you have to move fast. (See Bluff skill.)

Action: Usually none. Normally, you make a Stealth check as part of movement, so it doesn't take a separate action. However, using Stealth immediately after a ranged attack (see Sniping, above) is a move action.

Special: If you are invisible, you gain a +40 bonus on Stealth checks if you are immobile, or a +20 bonus on Stealth checks if you're moving.

Elves gain a +3 racial bonus on Stealth checks.

A Few Notes On How Stealth Works

Definitions:

Hidden vs Unseen: You are hidden if you have total concealment, total cover, or if you have used stealth successfully under less-than-total cover or concealment. You are unseen if you are invisible, or if your foe is blinded. Attacking while hidden denies the defender their AC bonus; attacking while unseen additionally gives you a +2 bonus to attack. NOTE: In general, you do not need to make stealth checks to remain hidden under total concealment or total cover. You also do not have to make stealth checks to stay unseen if you are invisible or if your foe is blind. However, you may choose to make stealth checks even in these situations to prevent a foe from pinpointing your location, or to break stealth.
Line of Sight: If you can draw a straight line from a creature to a target, with nothing blocking vision between the two points, then the creature has line of sight to the target. Line of sight may be limited by range, for example, a creature using standard darkvision only has line of sight within 60 feet. Line of sight is required for charging, using ranged weapons, casting rays, and targeting many spells, for example.
Direct Observation: In general, you can see all creatures and objects within line of sight, unless they are using stealth successfully.
Cover and Concealment: You can only use Stealth if you have cover or concealment (if does not matter if you have both). Every stealthy character should be familiar with the rules for cover and the rules for concealment.

Using Stealth: First of all, you have to have cover or concealment to make Stealth checks (exception: Hide in Plain Sight lets you use stealth even without cover or concealment). Stealth does not work if you start your round under direct observation, that is, if creatures are observing you using their primary sense (typically, sight). That means, as a rule, all creatures automatically see all other creatures within line of sight. For stealth to be useful, one of these situations must apply:

Start an encounter using stealth beforehand or start an encounter hidden or unseen. You can make stealth checks to remain undetected as rounds go by.
During an encounter, if you have ended the previous round under total cover or total concealment, you can use stealth when you emerge. You remain hidden so long as your stealth check beats the spot checks of others within line of sight, and from round to round so long as you are under cover or concealment after you are done with your actions.
During an encounter, if create a distraction to hide (see above), you can escape line of sight and become hidden.
If you start a round hidden, you can make a stealth check to remain hidden. Roll every round.

Attacking from Stealth: If you attack while successfully using stealth, your first attack gains the benefit of attacking while hidden, but after that attack you are revealed to all creatures within line of sight (exception, sniping). While you are using stealth to remain hidden, your foe is denied her dexterity bonus to AC. After that first attack, you are no longer hidden and you have revealed yourself. Note that if you are unseen (invisible, fighting a blind foe, etc), then your attack denies your foe her dexterity bonus and you gain a +2 to hit.

This means you can start a round hidden, emerge and move to a foe, make a stealth check, and then attack, even a melee attack, and gain the benefits of being hidden for that first attack (if the target's spot check does not beat your stealth).

Stealth Fails: You are no longer hidden if you attack, use a magic item that requires verbal activation, cast a spell with a verbal component, speak above a faint whisper, create a light or visual effect centered on yourself, or in some other way draw attention to yourself.

Lighting and Stealth: Ambient lighting makes a big difference in using stealth. In bright light you cannot make stealth checks based on concealment, only cover. In normal light you can make stealth checks based on cover and concealment, although in normal light the concealment needs to take the form of an impediment to vision, such as foliage or mist. In dim light you have concealment by definition, so you can make stealth checks simply based on the dim lighting. Note that creatures with low light vision have a +5 bonus to spot or search for creatures using stealth based on lighting, so you might be wise to also hide behind cover or physical concealment as well, if you can. In darkness you do not have to make stealth checks because darkness ends line of sight. However, if you suspect a creature with darkvision (or some other way to see through the dark) is in the area, you can still make stealth checks based on cover or physical concealment.