Skills

«Skills» are features/abilities that a person can use in a Lefa. These can be trained and leveled up to gain perks or abilities for the skill.

There are various types of skills in Sword Art Online, including: Support Skills, Combat Skills, Weapon Skills, Sword Skills, Extra Skills and Unique Skills. Players have also dubbed some techniques as Outside System Skills, though they are not actual skills system-wise.

ALfheim Online later imported Sword Skills from Sword Art Online and also developed a type of Sword Skill called Original Sword Skills.

Mods
Certain skills in Sword Art Online also have Mods (モッド). Mods can either be special bonuses that increase the effectiveness of the skill (e.g. decreasing Sword Skill cooldown time, increasing the range of the player's detection etc.), or various abilities (e.g. the Tracking mod for the Searching skill). It is known that at least for certain skills, like the One-handed Straight Sword, a new mod can be chosen every 50 levels of proficiency.

List of Known Skills in Astriea
In general, skills must be equipped in a limited amount of skill slots. A new player is given 2 slots to use, with more increments being rewarded after leveling up a few times.Skills may be trained up to level 1000, at which it is considered «Completed» (完全習得). There is rumored to be an unlimited number of skills in Astriea.

Support Skills

 * Acrobatics (軽業)- Determines a person's jumping height and the ability to perform aerial maneuvers. Bottom level is the natural jumping height for the person.
 * Blunt Weapon Forging (打撃武器作製) - The effectiveness with which a player can craft Blunt Weapons.
 * Drug Mixing (薬剤調合)
 * Equipment Appraisal (装備鑑定)
 * Extended Weight Limit (限界重量拡張)- Increases inventory size and weight capacity.
 * Familiar Recovery (使い魔回復)
 * Familiar Communication (使い魔交信)
 * Hiding - Allows for a person to disappear. Only works on targets that use visual tracking.
 * Light Metal Armor Forging (軽金属鎧作製) - The effectiveness with which a player can craft Light Metal Armor.
 * Metal Equipment Repairing (金属装備修理) - The effectiveness with which a player can repair metal equipment and tools.
 * Heavy Metal Armor Forging (重金属鎧作製) - The effectiveness with which a player can craft Heavy Metal Armor.
 * Metal Refining (金属精錬) - The effectiveness with which a player can turn raw ore into refined ingots of metal.
 * Musical Instrument (楽器)
 * Picking (鍵開け) - The ability to open locked chests and doors. The doors of rooms rented or owned by players cannot be affected by this skill.
 * Purchase Negotiation (買取交渉)
 * Reveal (看破)
 * Searching - A skill that determines the player's detection range. Allows finding monsters and players in hiding.
 * Tracking - A modification to the Searching skill which allows tracking monsters. Can also be used to track a player who is registered as a friend by displaying their footprints from a certain time.
 * Sales Negotiation (売却交渉)
 * Sewing (裁縫)
 * Slash Weapon Forging (斬撃武器作製) - The effectiveness with which a player can craft Slashing Weapons.
 * Straining (聞き耳) - The ability to hear sounds from further away than normal. Higher level of skill grants the ability to hear through locked rooms.
 * Sprint (疾走)
 * Thrust Weapon Forging (刺突武器作製) - The effectiveness with which a player can craft Stabbing Weapons.'''
 * Tools Appraisal (道具鑑定)<
 * Trap Dismantling (罠解除)
 * Woodcrafting

Combat Skills

 * Parry (武器防御)- The ability to use an attack to block an opposing strike. Maximum level makes it possible to destroy an item currently at less than half of the maximum durability; anything with a durability above that will not be damaged.
 * Howl (威嚇) - Attracts the attention of NPC monsters and increases a player's Hate value. Often used by tanks to lure enemies to the player.
 * Battle Healing (戦闘時回復)- Recover low amounts of HP over time during battle. It can be leveled up by constantly getting one's HP into the red zone.
 * First Aid (応急回復)
 * Meditation (瞑想) - «Extra Skill» Increases HP regeneration and decreases the remaining time of negative statuses by entering a mental concentration pose. Obtained in a 6th floor quest.
 * Light Metal Equipment (軽金属装備) - The effectiveness with which a player can use Light Metal Equipment.
 * Lightweight Shield Equipment (軽量盾装備)
 * Leather Equipment (革装備) - The effectiveness with which a player can use Leather Equipment.
 * Heavy Metal Equipment (重金属装備) - The effectiveness with which a player can use Heavy Metal Equipment.
 * Spiritual Light (霊光) (hate skill)
 * Fighting Spirit (気合)(hate skill)

Weapon Skills
See Also Sword Skills

In Sword Art Online, there are several different classes of Weapon Skills, each of which unlocks the use of Sword Skills in that category. There are generic weapon skills such as «One-handed Straight Sword» and «One-handed Curved Sword». Then, there are additional weapon skills that can be unlocked after fulfilling a certain set of conditions. For example, in the sword category, the «One-handed Straight Sword» skill must be trained quite a bit before «Rapier» and «Two-Handed Sword» appears on the weapon skills list.

Weapon skills that do not have clear conditions for appearing are called Extra Skills. There are roughly around ten known Extra Skills, including the «Katana Skill» wielded by Daniel. Each of these extra skills have at least ten people in the Sword Art Online world who practice the skill.

There are ten Unique Skills, which are weapon skills unique to a single player. So far only six of them have been revealed and only two of them are known to be acquired by a player. Additional Unique Skills were intended to be released beginning with the 90th Floor Aincrad.

Known Skills:
 * One-handed Straight Sword (片手用直剣)
 * One-handed Curved Blade (片手用曲刀)
 * One-handed Dagger (片手用短剣)
 * One Handed Rapiers (片手用細剣)
 * One-handed War Hammer (片手用戦槌)
 * Wild Dance (乱舞)(claws)
 * Two-handed Straight Sword (両手用直剣)
 * Two-handed Assault Spear (両手用突撃槍)
 * Two-handed Battle Axe (片手用戦斧)
 * Blade Throwing (投剣)
 * Martial Arts (体術) - An «Extra Skill» unlocked from a quest on the 2nd Floor which allows using Sword Skills with one's hands and feet - An «Extra Skill» that is unlocked by frequent usage of the One-handed Curved Blade and allows the usage of katanas.
 * Dual Blades - A «Unique Skill» given to the player with the fastest reaction time.
 * Holy Sword - «Unique Skill»
 * Darkness Blade - «Unique Skill»
 * Battoujutsu - «Unique Skill» Means "Sword Drawing."
 * Shurikenjutsu - «Unique Skill» Means "Concealed Weapons."
 * Infinite Spear - «Unique Skill»

Other Skills

 * Fishing - The effectiveness with which a player can catch fish. Higher levels catch rarer fish more often.
 * Cooking (料理) - The effectiveness with which a player can combine ingredients to create varieties of food, some of which can have medicinal properties. Higher level of skill allows the successful cooking of higher-ranked foods.

List of Known Skills in Arero Swords

 * Suggestion (弾道予測拡張)<ref name = V
 * First Aid (応急手当)
 * Acrobatics (軽業)
 * Hawk Eye (視力強化) - reduces the distance effect (allows zooming the player's vision) and increases the visual identification rate.
 * Weapon Creation (銃剣作製)
 * Knife Creation (ナイフ作製)
 * Army Combative (軍隊格闘術) - a skill that allows grappling in hand-to-hand combat.