For hints on using skills and example builds, see Builds.
Skills in PAYDAY 2 are divided among four skill trees: Mastermind, Enforcer, Technician, and Ghost. For each class, there are six tiers: Tier 1 is unlocked by spending 1 skill point on its parent class, Tier 2 is unlocked by spending 5, Tier 3 by spending 10, Tier 4 by spending 20, Tier 5 by spending 30, and Tier 6 by spending 40. 1 skill point is given each time the player gains a Reputation level, plus an additional 2 points at every level divisible by 10 (meaning that instead of just 1 skill point, 3 skill points will be granted at levels 10, 20, 30, 40 etc). Thus, once the player reaches the maximum Reputation level of 100, the player will have a total of 120 skill points.
Because the total skill points needed to unlock Basic and Ace for every skill in a tree totals 145 points, it is impossible to Ace every skill in even a single tree (and furthermore, there are four separate trees in total). Because of this, it is advisable to only spend points on specific skills you truly need and want, and to spread skill points over multiple trees if necessary. In fact, each skill tree has highly desirable utility skills in Tier 1 that only require a handful of skill points to obtain, thus it is expedient to obtain all these low Tier entry-level skills. Planning your build can be done with the skills calculator.
For each tier, there are three skills and an additional bonus for unlocking the tier. Each skill, after the Basic is obtained, can be Aced for further benefit. Skills in tiers 1 to 3 cost one skill point to unlock Basic and three skill points to Ace, whereas skills in tiers 4 to 6 cost four skill points to unlock Basic and eight skill points to Ace.
Tier bonus is considered active if it states that it is unlocked. It is considered unlocked when you can invest points into skills of that tier (skills are not grayed out). You do not need to actually invest any points into skills in that tier.
Party bonuses do not stack with the identical bonus coming from other players in the party that have the identical skill (thus it is somewhat sub-optimal for multiple players to get the same party-benefit skills, if you always play with the same team of players).
All other bonuses stack, unless stated otherwise, including bonuses from Basic and Aced versions of the skill.
The Mastermind is a manipulative leader who excels in situational control.
Spending the first point in the Mastermind skill tree unlocks the ability to place the doctor bag deployable. The doctor bag can be used to regain health. The doctor bag has 2 charges in its basic state.
Bonus: Increases your doctor bag interaction speed by 20%.
You gain 15% more experience for finishing days and jobs.
Ace (3 pt):
Your crew gains 30% more experience when you complete days and jobs.
Although the Skill description states that the XP bonus is applied to your crewmates, you yourself are considered part of the crew, and so when you take the aced skill, you gain the bonus as well. This stacks with the basic skill for a total 45% increase in XP earned. This bonus is reflected in the base figure shown by Crime.net when you are selecting a heist, though it is accounted for separately as "Skill Bonus" when the XP is summed up at the end of a heist.
You can convert a non-special enemy to fight on your side. This cannot be done during stealth and the enemy must have surrendered in order for you to convert it. You can only convert one non-special enemy at a time.
Ace (8 pt):
The converted enemy gains 65% more health and deals 45% more damage.
Taser shock attacks on you backfire, knocking back the Taser.
Ace (8 pt):
Interacting with an enemy Taser while he is electrocuting you will electrocute him, dealing 50% damage to his health.
Bonus: Your weapon stability with all weapons is increased by 5%. You gain 10% more armor. Reduces the armor recovery time for you and your crew by 10%. (Stacks with Tier 2 Bonus giving 10% total reduced recoil for all weapons).
The Ghost is a stealth artist, capable of grand theft without force or violence.
Spending the first point in the Ghost skill tree unlocks the ability to use the electronic countermeasure equipment, also known as the ECM jammer. When used, the ECM jammer can open ATM machines and temporarily cancel out electronic devices such as cell phones and cameras.
1 ECM jammer is added to your inventory. An ECM jammer lasts 20 seconds.
Bonus: Your chance to dodge bullets is increased by 5%.
You can now interact with ECM jammers to cause a feedback loop. When interacted, the ECM jammer has a 50%-100% chance to incapacitate enemies within 25 meters radius every 1.5 seconds. ECM feedback lasts 15-20 seconds.
Ace (8 pt):
You will now instantly interact with a ECM jammer and the ECM feedback duration is increased by 25%.
www.pd2skills.info offers a skill calculator that is useful for planning out skill progression, and was endorsed by Overkill.
With the Death Wish update, the value of durability-increasing skills like Iron Man, Bulletproof and Sprinter Ace are increased, helping to prolong survivability on Death Wish difficulty.
The Ace effects of Mag Plus does not apply to Sniper Rifles, the Bronco .44 and the Mosconi 12G, for balancing issues in the case of the former and technical reasons in the latter two (e.g. the Mosconi has only two barrels, adding an extra round would prove unrealistic). The durability of Saw blades are also not affected by this skill, despite having a numeric "ammo" count.