Weapon skill

Prior to Patch 4.0.1, weapon skill represented your proficiency with a particular weapon. Players started out with only a handful of weapon skills and had to visit weapon trainers to learn others. Once a weapon skill was learned, it needed to be improved through active use of the weapon. Now all classes start with the passive Weapon Skills ability, which grants all relevant weapon skills upon creation, making this mechanic obsolete.

Overview
Weapon skill represents your proficiency with a particular weapon. The basic formula for your maximum weapon skill at a particular level is (5 * level). Each attack which is not evaded has a chance to increase weapon skill, with low weapon skill, the skill gain rate is at or near 100%, however the skill gain change begins to sharply decrease once the weapon skill cap is approached. At 10% away from the cap, the skill gain chance is roughly 50%, and gaining the final skill point can take hundreds of swings. The chance per swing seems to be unrelated to weapon speed, making low speed weapons better. Instant attacks like Sinister Strike and Hamstring help to increase your weapon skill faster. Note that attacking Evading enemies will not increase your weapon skill.

It has been confirmed that intellect increases the rate at which weapon skills are learned. Before Patch 2.0, this was listed in the tooltip but was removed shortly after that. If you want to level a weapon skill, try asking for an intellect buff or using a scroll which can help the process. Similarly, equip any gear you have that has an Intellect bonus on it—if you're a paladin, put on your Holy gear and cast Blessing of Kings; if you're a shaman, put on your Elemental or Restoration gear.

In Patch 2.3, stats on melee weapons which granted an increase to weapon skill were replaced by an increase to expertise rating. Items which granted ranged weapon skill increases instead now grant increases to hit or critical strike rating.

Player attacking a mob
If your weapon skill is LESS THAN OR EQUAL TO the mob's Defense skill (the mob's level * 5)


 * The base chance for your attack to miss the mob:
 * If the difference between the mob's Defense Skill and your Weapon Skill is less than or equal to 10 then the formula for calculating your base miss chance against that mob is: 5% + (Defense Skill - Weapon Skill)*.1%
 * If the difference between the mob's Defense Skill and your Weapon Skill is greater than 10, then the formula for calculating your base miss chance against that mob is: 6% + (Defense Skill - Weapon Skill - 10)*.4%


 * The base chance for your attack to be a critical strike is: 5% - (Defense Skill - Weapon Skill)*0.04%


 * The base chance for your attack to be dodged by the mob is: 5% + (Defense Skill - Weapon Skill)*.1%


 * The base chance for your attack to be parried by the mob:
 * If the difference between the mob's Defense Skill and your Weapon Skill is less than or equal to 10, your base parry rate is: 5% + (Defense Skill - Weapon Skill)*.1%.
 * If the difference between the mob's Defense Skill and your Weapon Skill is greater than 10, your base parry rate will be much higher. Exact figures are not known, but base parry rates of Boss mobs (effectively level 73 when attacked by level 70 players) are estimated to be between 10-15%, and may vary from one Boss to the next.


 * The base chance for your attack to be blocked by the mob is probably the same as the base dodge rate, i.e.: 5% + (Defense Skill - Weapon Skill)*.1%

Applying these formulae gives the following base miss rate for a Level 80 character with a 400 Weapon Skill:


 * v. Level 80 mob: 5.0% / dual-wield: 24%
 * v. Level 81 mob: 5.5% / dual-wield: 24.5%
 * v. Level 82 mob: 6.0% / dual-wield: 25%
 * v. Level 83 mob: 8.0% / dual-wield: 27%

At level 80, 32.79 hit rating reduces your chance to miss by 1%.

Thus if you are a Level 80 character with a Weapon Skill of 400, you need a Hit Rating of 263 (8.00%) to never miss a shot against a Level 83 boss (or skull mob) with a special attack or single-wield auto-attack. What this means is that there is a big +hit benefit to keeping your Weapon Skill within 10 levels of the mobs you are trying to fight. For example, by improving your Weapon Skill from 390 to 395, you effectively reduce your chance to miss against Level 81 mobs by 3%! However, after getting to 395, increasing your Weapon Skill the next 5 levels, to 400, only reduces your chance to miss by an additional 0.5% (or 3.5% in total).

Prior to 3.0, the base miss chance when your target's defense was 11+ points higher than your weapon skill was 1% higher. Back then, there was a huge jump in miss rate reduction by going from, say, 349 to 350 Weapon Skill. This was the point where you switched from one formula to the other, and so this particular single point of Weapon Skill was worth a dramatic +1.4% hit against a Level 73 mob/boss.

If your weapon skill EXCEEDS the mob's Defense skill, i.e. if the mob is lower level than you are


 * The base chance for your attack to miss the mob is 5% - (Weapon Skill - Defense Skill) * 0.04%.
 * The base chance for your attack to be a critical strike is 5% + (Weapon Skill - Defense Skill) * 0.04%.
 * The base chance for your attack to be dodged by the mob is 5% - (Weapon Skill - Defense Skill) * 0.04%.
 * The base chance for your attack to be parried by the mob is 5% - (Weapon Skill - Defense Skill) * 0.04%.
 * The base chance for your attack to be blocked by the mob is 5% - (Weapon Skill - Defense Skill) * 0.04%.

I.e., for each point that your weapon skill exceeds your opponent's defense, your chance to miss, be dodged, be parried, and be blocked decreases by 0.04%, and your chance to crit increases by 0.04%. Effectively, you can consider weapon skill to be the inverse of the defense skill.

Glancing Blows
Against mobs with defense roughly equal to or higher than your Attack Rating (i.e. your weapon skill), you will have a chance to land a glancing blow instead of a normal hit. A glancing blow only occurs on white melee damage, cannot crit, and does less damage than a normal blow. If the attacker's weapon skill is less than his level * 5, the damage reduction will be proportional to the difference between the attacker's weapon skill and the target's defense.

Back before patch 2.0, when Weapon Skill could be raised above your level * 5 from gear or racial bonuses, the damage reduction when a glancing blow occurred was reduced somewhat for each point of additional Weapon Skill. This is no longer the case.

Mob attacking a Player
If a mob's weapon skill (its level * 5) is EQUAL TO your defense, and you have no gear or talents that increase any of your defensive Ratings:


 * Its chance to miss you is 5%.
 * Its chance to score a critical strike against you is 5%.
 * Your chance to block the attack is 5%.
 * Your chance to parry the attack is 5%.
 * Your chance to dodge the attack depends on your Agility.

For each point that the mob's weapon skill (its level * 5) exceeds your defense, it gains the following:


 * Its chance to miss decreases by 0.04%.
 * Its chance to score a critical strike increases by 0.04%.
 * Your chance to block the attack decreases by 0.04%.
 * Your chance to parry the attack decreases by 0.04%.
 * Your chance to dodge the attack decreases by 0.04%.

For each point that the mob's weapon skill (its level * 5) is less than your defense:


 * Its chance to miss decreases by 0.04%.
 * Its chance to score a critical strike increases by 0.04%.
 * Your chance to block the attack decreases by 0.04%.
 * Your chance to parry the attack decreases by 0.04%.
 * Your chance to dodge the attack decreases by 0.04%.

Crushing Blows
If a mob's weapon skill (its level * 5) is at least 20 points higher than the target's level-capped defense (the target's Defense skill capped at its level * 5), there is a chance the target will receive a Crushing Blow.

Dazed
If a mob hits a target from behind, and the target takes damage from the hit that isn't Absorbed, there is a chance the player will be Dazed. The base chance for a level 30+ target to be dazed when hit from behind, if the mob's weapon skill is equal to the target's defense skill, is 20%. This chance can get as low as 0% if the target's defense is high enough, or as high as 40% if the target's defense is low enough. If the target is below level 30, it's base chance to be dazed is less; a level 10 target with fully trained defense skill only has a 7% chance to be dazed when attacked from behind by a level 10 mob.

Note that your defense skill is NOT level-capped for purposes of determining your chance to be dazed. It is possible to become undazeable while wearing tank plate gear.

Player attacking a Player
Weapon skills are maxed in PvP combat. This means leveling a weapon skill for pvp is unimportant; when attacking an enemy player, your Weapon Skill will always be considered to be your level * 5, and your target's Defense will always be treated as his level * 5 (before any Defense Rating from your target's gear is added in).

Weapon skill does not affect your chance to hit other players in the battlegrounds or in the arena, but it still affects your hit chance against enemy players in world PvP or duels.

Increasing your weapon skill (at level 70+)
A good place to increase ranged DPS for higher level characters is Plague Sprayer in Zul'Drak. They are level 80 Elites that fly above Kolramas. They have a high amount of health and the only attack they have is a plague beam that shoots straight down.

The Primordial Drake Eggs in Sholazar Basin also work well for this; they are high 70's, and do not attack back.

For ranged DPS (bows/guns) - Dr. Boom used to be an excellent choice - just bring enough ammo, and attack at will. Hunters had the best options with him due to auto-shoot. This no longer works as of 3.2. Likewise, the unkillable Servants in the Blasted Lands no longer skill you up when they are in their unkillable state.

Vendors in Dalaran sell white, low DPS weapons with extremely low attack speeds, making them great options for levelling weapon skill.

If you have a relatively good health pool, you can skill up from the waves of creates inside the Violet Hold:
 * Get some health restoring effects (here, here, here, or here, for example)
 * Set the difficulty to Normal.
 * Zone in and do not start the event.
 * Skill up by attacking the level 75 elite creatures, avoiding any which do too much damage for you to survive (this is not a problem at higher levels).
 * You can pick a portal and stand near it to fight everything emerging from it. If you get overwhelmed, retreat to the friendly NPCs by the doorway (or stay there the whole time).  If you get into too much trouble, run out!

Historical effects of weapon skill
The effect of weapon skill has changed several times over the game's history. Prior to patch 2.0, some items granted extra Weapon Skill directly, making it possible to have a weapon skill in excess of your level * 5. Back then, the formula shown above for your weapon skill exceeding your opponent's defense also applied in the reverse situation, i.e. when your weapon skill was less than your opponent's defense.

After the Burning Crusade went live, but prior to patch 2.1, CM Crezax made a post on the EU forums outlining the effect of weapon skill on higher-level mobs. Note that this refers only to monsters 3 levels higher than the player in PVE (i.e. boss level mobs). Corresponding numbers for 1 and 2 levels higher than the player are not known, but are likely lower.

Let's say you increase your weapon skill by 4.

Against a mob 3 levels higher than you, you get: 0.8% lower chance to miss, 0.4% lower chance to get dodged, 2.4% to be parried, and a 0.8% higher chance to crit.

These numbers given by the CM were questionable, and were rightly taken with a grain of salt.

Additionally, the Patch 2.0.1 notes said:


 * The player will gain 0.1% to their critical strike rating per weapon skill against monsters above their level.

Presumably this was only for Weapon Skill over your level's natural cap (Level * 5), a state of affairs which no longer exists as of patch 2.3. It was not known if you also got the additional 0.04% crit chance per additional +skill.

Since items with Weapon Skill or Weapon Skill Rating used to reduce your chance to miss, to be dodged, to be parried, and to be blocked, they could increase your "crit cap" as described in the Critical strike article.

Itemization
Prior to patch 2.3, a few items in the game granted the wielder Weapon Skill Rating. Even then, though, itemization for +weapon skill was spotty.

2.0.1 Skill Rating conversion Prior to patch 2.0, instead of Weapon Skill Rating, items granted their wielder Weapon Skill directly; e.g. a mace might say "Increases your skill with maces by 5." Under the new combat rating system introduced in 2.0.1, those items now all had a Weapon Skill Rating bonus instead.

It took 2.5 points of Weapon Skill Rating at level 60, and 3.9 points of Weapon Skill Rating at level 70, to increase your actual Weapon Skill by 1.

In applying the miss rate formulae listed in the "Chance to Miss" section above, fractional Weapon Skill levels were dropped, not rounded. So, say you had are a Level 70 character, and you equipped a piece of gear that gave +15 Mace Skill Rating. In theory, this equated to 3.8 +Weapon Skill. And, in theory, Blizzard could have used the fractional .8 in its subsequent calculations of hit and miss, or, perhaps, rounded it to 4.0. But it didn’t work that way. Instead, the fractional .8 Weapon Skill was simply dropped altogether. You got 353 Weapon Skill for purposes of all hit and miss calculations.

Another interesting point was that if you are able to stack your Weapon Skill above 365 at level 70, you'd find that each additional point of Weapon Skill above 365 continues to decrease your chance to miss by .1% per Weapon Skill level. So if your Weapon Skill was 366, your chance to miss was 4.9%, if 367, 4.8%, etc.

Pre-2.3 Talents
Rogues:


 * Weapon Expertise talent increased skill with Swords, Fists, and Daggers by 5 (rank 1) or by 10 (rank 2).
 * Mace Specialization talent increased skill with Maces by 2 per talent point spent (max 10).

Warriors:


 * Weapon Mastery talent increased skill with all weapons by 2 (rank 1) or by 4 (rank 2).

Paladins:


 * Combat Expertise talent increased skill with all weapons by 2 per talent point spent (max 10).

Pre-2.3 Racial Bonuses

 * Humans: +5 sword skill, +5 mace skill, +5 two-handed sword skill, +5 two-handed mace skill
 * dwarves: +5 gun skill
 * Orcs: +5 axe skill, +5 two-handed axe skill, +5 fist weapon skill
 * Trolls: +5 bow skill, +5 throwing weapon skill