Basic Spy strategy

The Spy specializes in deception and excels at punishing mistakes made by the enemy team. Although he is fragile and possesses some of the weakest weapons in the game, he can backstab enemies and sap Engineer buildings. The Spy will almost always operate behind enemy lines. To aid in this, he can use Cloaking and disguises to move about undetected. The ability to see enemy names and health levels allows him to pick off weakened foes with his Revolver. Because of the threat he poses, enemies will frequently Spy-check their teammates. The Pyro's flames nullify both Cloaking and disguises, making him the most dangerous counter-class to the Spy. A good Spy will use both his Cloaking and Disguise Kit to avoid drawing enemy attention.

Primary Weapons

Revolver / Big Kill

Although weaker than other primary weapons, the Revolver is extremely accurate, so you can use it to pick off weakened enemies from a distance. There are several situations where you'll choose it for combat over the Knife, such as when your backstab fails, you cannot safely approach a target, or when a Sniper has a Razorback equipped.

Ambassador

Use the Ambassador if you are confident about your aim. The ability to headshot lets you take out most classes in only a few shots and pairs well with your ability to see enemy health. There is a set period after firing where the Ambassador cannot headshot, so it's better to space your shots out instead of firing rapidly.

L'Etranger

L'Etranger converts firepower into potential fleeing power and can be used to safely refill your Cloak from a distance. It pairs well with the Cloak and Dagger or Dead Ringer, watches that have their recharge methods restricted.

Enforcer

The Enforcer's increased damage output is useful if you have to fight your way out of enemy lines and makes you a greater threat in one-on-one duels. However, the increased time it takes to activate your Cloak makes it easier to be tracked if an enemy discovers you. The Dead Ringer is not affected by the Enforcer's downside and will still instantly Cloak you upon taking damage.

Diamondback

The Diamondback's decrease in base damage makes it a poor weapon for direct encounters. However, the guaranteed critical hits gained upon the destruction of a sapped building allow you to more easily escape from enemy territory after a successful attack. Work with your allies to ensure that buildings are destroyed; for example, if an Engineer is actively guarding his nest of buildings, simply disable his Sentry Gun and run interference while your teammates destroy it. You will still recieve critical hits, even if the final hit wasn't done by your Electro Sapper.

Secondary Weapons

Electro Sapper

The Electro Sapper will instantly disable an Engineer's building and can only be removed by the Engineer or the Pyro's Homewrecker. You have an unlimited supply and can place them rapidly on any building within melee range. Typically, you'll first backstab an Engineer, then quickly sap any nearby buildings to prevent them from firing at you. Your weapons deal reduced damage to any building that has an Electro Sapper on it.

Melee Weapons

Knife/Saxxy

The Knife deals pitiful damage. Unless you can backstab an enemy, you're probably better off using your Revolver in fights, especially after you've been discovered. However, if only a little more damage is required to kill your target, the Knife makes a reliable finisher.

Your Eternal Reward

The inability to initially disguise will make you rely more on your Cloak ability to find good hiding places. Once you obtain a disguise, you are free to approach your enemies from behind. Do not rely on the "silent killer" aspect of the weapon; dead enemies will still be able to communicate using text or voice chat. If you're stuck with a slow disguise, you can Cloak or attack at any time to move at normal walking speed.

Conniver's Kunai

The Conniver's Kunai's health reduction will make you very, very frail. Unless you are under the effects of its overheal, you can be killed by just one stray projectile. When using the Conniver's Kunai, play aggressively and try to land continuous backstabs to maintain your health and eliminate any negative status effects such as afterburn. Using the Dead Ringer in conjunction with the Conniver's Kunai will allow you to quickly navigate behind enemy lines without dying to a random shot.

Big Earner

The Big Earner's health reduction does not make you as frail as the Conniver's Kunai but still allows you to instantly be killed by stronger weapons like the Soldier's Rocket Launcher. Play aggressively and get multiple kills to rapidly charge your Cloak for an easy escape. It pairs well with the Cloak and Dagger, which cannot be recharged using pickups, as well as the Dead Ringer, which will allow you to navigate behind enemy lines without dying to a random shot.

PDA 1

Disguise Kit

The Disguise Kit is one of your major infiltration tools. If near allies, it's best to disguise as another friendly class or an enemy Spy so that even if seen by an enemy, you will draw less attention. You can safely change your disguise while cloaked to throw off enemy suspicion. A disguise takes one second to become effective, so avoid the common mistake of approaching an enemy before the change is complete. Once you have successfully navigated behind enemy lines, try to not behave like a Spy; for example, reloading your Revolver while disguised will mimic your disguise's reload animation, allowing you to better blend into an enemy crowd. Even if you're disguised, don't linger in front of enemies for too long, as you are still vulnerable to Spy-checking.

PDA 2

Invisibility Watch / Enthusiast's Timepiece

Out of all your watches, the Invisibility Watch has the smallest margin of error but allows you to cover the furthest distance while invisible. To keep your Cloak filled and ready for emergencies, deactivate it when in safe areas and frequently grab metal pickups. Although you are invisible, you are not invincible; upon seeing an ammo box disappear, competent enemies may Spy-check the area. If in enemy territory, always stay on the move to decrease the chances of you being detected or cornered.

Cloak and Dagger

The Cloak and Dagger is best used in areas with few metal pickups. By remaining still, you can stay invisible indefinitely, allowing you to camp an area to pick off important targets, such as enemy Medics. When traveling to a location over a set period of time, moving slowly or in quick bursts will drain the same amount of Cloak. Continue to be mobile; enemies will be encouraged to Spy-check if you stay in the same area too long. Likewise, don't just use the Cloak and Dagger to stay out of harm's way; being alive does not necessarily mean being useful.

Dead Ringer

Simply "dying" from fall damage is a sure sign that you're a Spy. To make your feign death more convincing, consider letting the enemy damage you for a bit before taking out the Dead Ringer. Even if you make your feign death completely obvious, the Dead Ringer's damage reduction while cloaked allows you to easily navigate across battlefields and behind enemy lines. While enemies will not see you if you bump into them, you are still vulnerable to revealing effects such as fire, bleeding, and Jarate. Know where metal pickups are so that you can quickly refill your Cloak for emergencies.

Item sets

The Saharan Spy

Your Eternal Reward removes your ability to disguise, forcing you to rely on your Cloak, while the Saharan Spy item set's increased Cloak blink time makes you visible for a longer period of time if an enemy manages to temporarily reveal you. However, if you can successfully get behind your enemies without being caught, the significantly reduced decloak volume makes finding suitable hiding places easier. The Dead Ringer is not affected by the item set's downsides, as its Cloak never shimmers.

The Man of Honor

The Man of Honor set item focuses on an aggressive playstyle. The Big Earner allows you refill and repeatably use your Cloak when on a killing spree while the Enforcer's increased damage makes directly fighting enemies easier.