Spy checking

A BLU Pyro successfully Spy checks teammates leaving their spawn area on Harvest.

“

Hard ta stab a guy in da back when he's beatin' ya freakin' head in, huh?

Click to listen

— The Scout on anti-espionage.

”

Spy checking is a common term for the investigations players make to determine where or who enemy Spies are and eliminate them. These investigations are both useful and important because Spies cannot attack while cloaked, cannot immediately attack or place Sappers after decloaking, and can effectively kill by attacking from behind. The process can be somewhat complicated because disguised Spies can use the Dead Ringer to make a hasty escape when discovered.

Identifying Spies

General Strategy

The easiest and often preferred way to Spy-check is to simply shoot a teammate. Real teammates take no damage at all, while enemy Spies die after a few shots.

Remember that players on opposite teams cannot pass through each other. Bumping into teammates indicates that player is an enemy Spy.

Look for teammates that are behaving bizarrely. Players in unusual positions, moving in the wrong direction, deliberately avoiding contact with teammates, or hiding in corners should all be Spy checked.

Pay special attention to areas with health kits or ammo boxes or corners, nooks and spots that players usually do not enter. Spies tend to use these areas to hide in while they recharge their Cloak.

Watch for teammates who are not firing their weapons. Spies cannot fire their weapon without removing their disguise.

Keep an eye out for shrouds of smoke that are colored red or blue. When a Spy uses the Disguise Kit, it takes a moment for the disguise to activate, during which the Spy will be shrouded in team-colored smoke.

If you are dead, you can cycle through different camera angles around the map while waiting to respawn. Look out behind teammates or on open points for Spies uncloaking or disguising. You can then alert teammates or Spy-check where you last saw the Spy.

Class-specific strategies

Scout

The Scout is the fastest class. Because of this, one effective strategy is to run around the map and try to bump into fellow teammates. As noted above, any teammate that cannot be passed through is an enemy Spy in disguise.
Some of the Scout's melee weapons can be used to Spy-check effectively. Refer to these and their individual articles for details.
Mad Milk will reveal disguised and cloaked Spies, since a coated Spy will be visible by white drips.

Soldier

The Soldier has no particular Spy-check strategies apart from the general ones. Spy-checking by simply shooting rockets at suspicious players is very effective because of the high damage your rockets do at close range.

Pyro

The Pyro's ability to set enemies on fire with incendiary weapons is perhaps the most useful tool for detecting Spies, since only enemies can be ignited. This is the most reliable method of Spy checking teammates. The team-colored glow produced by a burning player is especially visible when surrounding a cloaked or disguised Spy. It is recommended to use only small bursts to Spy check to conserve flamethrower ammunition.
The Compression blast is also useful in revealing Spies, as well as stopping attempts to escape. Teammates will not be affected by compression blast, so any teammate that can be pushed by it is a Spy. While flames are normally more efficient, compression blasts can be used to push Spies away from your teammates if they are in danger of being backstabbed.
If a Spy is using the Dead Ringer, they may appear to die instantly from your flames. Spray fire in the vicinity to try and reignite a Spy who has feigned death. Pursue them until you are certain of their death.
Know that the Spy-cicle greatly aids Spies trying to escape or stay hidden. Be aware of its use and counter it with other weapons if necessary.
- The noise a Spy-cicle makes when extinguishing flames is very distinct. Learn to recognize it, both when the Spy is cloaked and when they are disguised as a teammate.

Demoman

Placing Stickybombs over a wide area can cause Spies to hesitate about traversing such minefields. Teammates will almost always simply pass over the Stickybomb trap.

Heavy

Because movement speed is greatly reduced for a spun-up Heavy, they are tempting backstab targets. This can sometimes be used as a goad for enemy Spies to approach. Act unaware, then turn around to surprise a possible Spy.
As Heavies are often coupled with Medics, Spies place great priority upon stabbing the Medic first, then the Heavy as to deny the team the Medic's support. Turn around quickly if you hear your Medic die from a backstab.

Engineer

Keep an ear out for Sapper notifications; if one happens while a teammate is standing near the sapped building, that teammate is probably a Spy.
Spy-check suspicious players that approach your buildings with the Pistol. The Shotgun can also be used, but its ammo is often needed for other threats. Avoid chasing the Spy with your Wrench, as it leaves your buildings vulnerable. The Wrench is also bad for Spy-checking since it prioritises repairs over combat, meaning buildings will always be hit instead of players next to them.
If any teammate is unable to pass through a Sentry Gun or Dispenser, that teammate is a Spy. Placing these buildings in narrow passages can severely limit the damage a Spy can do to them or you.

Medic

As a Medic, Spies can use you to gain health while disguised. If you are particularly suspicious of a player, do not heal them. Spy-check them with your melee weapon or have your patient deal with them for you.
Spies may target you while you are healing a patient. Watch your back while healing. You can also have your patient Spy-check for you, though this may be difficult during intense battles.
Spies may also simply head directly for your patient rather than yourself. If a teammate seems to be making a beeline for your patient's back, warn them of a possible Spy.
Avoid chasing Spies too much - your ability to heal is generally more useful. Spies can also trick you this way into ambushes, so be careful. Your patient is generally more suited to killing the Spy than you are.

Sniper

Snipers tend to be particularly unaware of their surroundings while zoomed in. Switch positions frequently and check your surroundings as you do so.
Jarate is a particularly useful Spy-check weapon, as it reveals both cloaked and disguised Spies. Use it to Spy-check suspicious teammates.
The Razorback will prevent a Spy from backstabbing you, but doesn't protect you from being shot! Be careful when separated from your team, even with this weapon.

Spy

Spies are generally poor Spy-checkers, because they deal poor ranged damage and use tools to escape quickly. Although their backstab is very useful to protect teammates as it kills instantly, Spies spend their time best among the enemy and rarely encounter one-another.

Revealing cloaked Spies

When cloaked, Spies will momentarily appear and flicker in their team color upon being damaged or when bumping into enemy players. Keep an eye out for when a Spy is revealed this way. Strafing while navigating corridors makes it difficult for a cloaked Spy to pass safely.
- Note that The Dead Ringer greatly diminishes this drawback.

Shooting into common Spy hiding places may reveal an unlucky Spy.

Try to listen for the sounds Spies make while cloaking and decloaking. If you hear a characteristic cloaking sound, a Spy may be nearby.

An item that disappears without a player picking it up may indicate that it was picked up by a cloaked Spy. Spy-check nearby to reveal any careless Spies.

In places with water, look for floating water drops. Players climbing out of water will be visibly dripping with it, including cloaked Spies.

An automatic door that suddenly opens without any visible player being nearby indicates a cloaked Spy passing through.

Protecting an Engineer's buildings

Since an Engineer's buildings are a major target for Spies, specific strategies may be more effective around Engineer's buildings:

Spy-check suspicious players that approach a friendly Engineer's buildings. Spies trying to sap buildings often run straight towards them. You can body-block Spies to prevent them from placing a Sapper.

As a Pyro, use Dispensers to constantly refill the ammo of your flamethrower. Use this ammo to create a constant firewall that Spies cannot safely pass through or to constantly Spy-checking the area. Heavies can also make use of Dispensers in this way.

As a Demoman, Stickybombs can be placed around friendly buildings to kill Spies who try to sap them. Place a few bombs around an Engineer's buildings and detonate them when you hear the Engineer announce that his buildings are being sapped.

As an Engineer, if a Teleporter is being sapped from its entrance, you can Spy-check the next player teleporting through once you remove the Sapper. This may be an enemy Spy trying to telefrag you, so be careful not to stand on top of it. Turning the telefrag attempt into your own surprise can be quite humiliating to enemy Spies.

Identifying enemy Spies

Various team-colored indicators definitively determine an enemy Spy or a friendly one, including:
- The flicker a cloaked Spy makes when being bumped or injured.
- The fading a cloaked Spy does while cloaking or uncloaking.
- The glow a player on fire makes.
- The smoke from a recent use of the Disguise Kit.

Signs that definitely indicate an enemy Spy, or lack thereof

Common signs

A 'teammate' that cannot pass through another teammate, or conversely, a 'teammate' that has been observed walking through an enemy.
A 'teammate' that asks for Medic and has "wrong" cross background colour. For example, Pyro at full health having its background red like on heavily injured teammates, or near-dead Heavy having it white.
A 'teammate' who cannot enter areas open to your team (such as supply rooms), or conversely can enter areas forbidden to your team.
A 'teammate' placing Sappers on friendly buildings.
A 'teammate' standing on a friendly Sentry Gun or Dispenser, or who cannot pass through them, and is not the Engineer who owns the building.
Two people that have the same name. One (or both) of them is a Spy.
Seeing or hearing a voice command attributed to yourself without you having used it, or more importantly, seeing "yourself" moving around.
A 'teammate' that is known to be dead or elsewhere.
A 'teammate' who has a name that does not correspond with his or her current class on the scoreboard. This happens when a Spy disguises as a class not currently on the team, or if the person has changed class while the Spy was disguised.
A health or ammo pickup that vanishes without cause; this means a cloaked Spy has grabbed it.
A 'teammate' on an uncontested control point or near the cart on Payload maps who does not seem to be capping the point or pushing the cart (assuming the point is available for capture by that team).
A non-Spy 'teammate' that is being ignored by an enemy Sentry Gun.
A non-Spy 'teammate' that is being healed by an enemy Medic or Dispenser.

Class- or item-based signs

A burning Pyro, as genuine Pyros cannot be ignited.
A Scout or Medic running slower than they should.
A 'teammate' being soaked by friendly Jarate or Mad Milk, or not being affected by the enemy's.
An enemy Scout that is capping a point at ×1 speed is a Spy disguised as one of his allies.

Signs that possibly indicate an enemy Spy

None of these indicators are conclusive proof of a Spy, but all of them would make a good time to run a Spy check:

Common signs

A teammate trying to stay behind other teammates, as if trying to backstab them.
A teammate not firing at the enemy.
A teammate who is in the direct firing line of an enemy but is not being fired at.
A teammate who retreats backward upon seeing other teammates, while still facing those teammates.
A teammate who appears to be dodging your team's attacks or backpedals immediately after seeing loose grenades or a carpet of friendly Stickybombs.
A teammate that deliberately avoids walking through other teammates, especially in tight corridors. Spies will strafe and dodge other players to avoid bumping into them.
A teammate with an entirely stock loadout (occurs when a Spy disguises as a class the team does not have).
A teammate being attacked or accused by real teammates who believe the player is a Spy.
A teammate holding their primary weapon for longer than they should. In particular, it is unusual to see Spies, Engineers, Medics and Demomen holding their primary weapons for long, as they prefer other weapons.
A teammate hanging around areas that are advantageous to Spies, such as dark corners and nooks.
A teammate that isn't displaying the player's usual behavior.
Someone standing still at a distance from the rest of the team. This could be a Spy trying to line up an Ambassador headshot.
A teammate that appears to be looking more at your team than at the battle.
Being suddenly blocked for no apparent reason. This may indicate a cloaked Spy passing through.
A teammate suspiciously near Sentry Guns, especially if they are attempting to move behind the Engineer tending them.
A teammate acting inappropriately for their class, such as an Engineer at no nearby buildings or a Sniper near the Intelligence.

Class- or item-based signs

A Medic who isn't healing anyone.
A Heavy that does not spin his primary weapon when enemies appear.
A Sniper who does not stop to zoom in and take shots.
An Engineer that does not appear to be upgrading or repairing buildings.
A Spy who is not amidst the enemy.
A Medic without any Übercharge built up.
A person you know that is using a weapon that they don't normally use (i.e. a friend who normally uses the Huntsman, but appears as using the stock Sniper Rifle; meaning a Spy is disguised as a Sniper when your team doesn't have any) or not wearing hats if they wear them (again Spy disguised as a class your team doesn't have)

Signs that indicate a teammate is not an enemy Spy

These actions prove that a teammate is definitely not an enemy Spy. Performing any of these is a good way to inform your teammates that you are not an enemy Spy.

Common signs

Any usage of a weapon or item (taunting, shooting, swinging, scoping, eating, drinking, etc). This does not apply to reloading, however, as Spies are able to imitate a reload by reloading their Revolver whilst disguised.
A teammate that passes through other teammates, or yourself, as opposed to being stopped. (However, this can also happen if both teammates are enemy Spies).
A teammate entering an area forbidden to the enemy, such as resupply rooms.
A teammate who appears to take damage from enemy fire.
A non-Engineer who can pass through friendly buildings.
A teammate that is carrying the enemy team's Intelligence or capturing a control point for your team.
A teammate saying certain responses which a Spy cannot imitate himself.
A teammate that can be spectated. Note that a few servers allow spectating enemy players.
In Mann vs. Machine mode, a teammate that jumps. Spy Robots never jump.

Class- or item-based signs

Any usage of class-specific abilities, e.g. Scouts double jumping, Heavies spinning their Minigun, Snipers that are scoped in, etc.
A Scout or Medic moving at his normal movement speed.
An Engineer holding a PDA or a toolbox (for whatever reason).
A Spy holding their Sapper or Disguise Kit.
A Spy without a mask on (not disguised).
A Medic with any amount of Übercharge built up.

Spy-checking Spies with items

Main article: Anti-Spy strategy

Dealing with the Dead Ringer

The Spy has the ability to feign death with one of his unlockable items, the Dead Ringer, so always be wary upon killing enemy Spies as they may still be alive elsewhere. Thus, it's best to know some of the signs that tell that the Spy may not really be dead. Spies using the Dead Ringer cannot manually Cloak, and cannot use any weapons while the Dead Ringer is out.

If an enemy dies upon the first hit while approaching friendly lines without firing his weapon, it is most probably an enemy Spy disguised as one of his teammates. Most players don't run in with such low health, and a Spy disguised as a teammate will drop a corpse of the class he was disguised as.
- Similarly, if an obvious enemy Spy disguised as a teammate approaches the front lines from the enemy's position, he is most likely using the Dead Ringer, even if he doesn't die from the first hit. Remember that the Dead Ringer cannot Cloak at will, so a Dead Ringer Spy will rely on opponents' fire activating his feign death in order to become invisible.
- In general, if a player that has been identified to be an enemy Spy seems to be approaching a teammate suicidally, he is probably trying to get damaged so that his Dead Ringer will be activated, so don't be fooled.

The decloaking sound of the Dead Ringer is highly distinctive, but requires players to be within a certain distance to hear it. Listen for it.

Picking up the Spy's dropped weapon does not replenish ammo or metal. This is an easy way to double-check if a recently-killed Spy is using the Dead Ringer or not.

Being stopped while moving and not bumping into any visible objects can mean that a Spy whose Dead Ringer was activated is trying to pass through.

If the Spy uses his Disguise Kit shortly before being "killed," the smoke effects will follow the Spy for the time that it takes for the Disguise to be equipped. Therefore, try to track any smoke that continues to move after an enemy Spy was killed.

If it is safe to do so, stand still after "killing" a Spy known to use the Dead Ringer. This may provoke the Spy into uncloaking nearby and making himself vulnerable. You can also check the scoreboard during this time, to see if the Spy "respawns" much faster than they should be able to.

Dealing with the Cloak and Dagger

The Spy's Cloak and Dagger allows him to stay cloaked indefinitely, and to hide in unconventional places while waiting for the right time to strike. An area that may seem impossible for a Spy to hide in may be sheltering a particularly cunning Spy who knows where the enemy team will not check for Spies.

In general, most Cloak and Dagger Spies will try to hide in corners in order to avoid being bumped into as they recharge their Cloak. Try to occasionally fire into corners or vantage points with wide fields of view.

One brute-force method for dealing with the Cloak and Dagger is to simply repeatedly check an area where the Spy is hiding. As the Cloak and Dagger has an extremely short charge meter, the Spy cannot make too many movements or their Cloak will run out.

Some unconventional Spies will hide out in the open rather than against walls or in corners. This allows them to maneuver easily to avoid detection, and easily avoids the most often checked areas of a map. Try to keep this in mind if a Spy is suspected to be in the area.

Dealing with Your Eternal Reward

While Spies using Your Eternal Reward cannot use their Disguise Kit at will, they make up for this by being able to quietly Backstabbing any enemies and leaving no body for their teammates to find. A Spy using Your Eternal Reward can be impossible to detect even when he is killing teammates nearby.

Because they cannot use their Disguise Kit, simply identifying the last player that the Spy Backstabbed will let teammates know which player and class may be the Spy. Note that Spies with Your Eternal Reward equipped can still change their disguise weapon.

If backstabbed by the Spy, clearly announce this to teammates, as well as the class that the Spy is now disguised as, to make sure that they know who the Spy is disguised as.

When the Spy Backstabs his victim, the faint sound of the melee hit can be heard if close enough. This can serve as a key warning that a Spy might be killing teammates in the immediate vicinity.

Remember that any kills made using Your Eternal Reward will not generate kill reports for the opposite team. Pay very close attention to teammates' movements and listen for any melee hit sounds nearby.

When a Spy with the Eternal Reward backstabs a teammate, the teammate's body disappears. However, their weapon remains sitting on the ground. If you see one of your teammates and their weapon on the ground, it's not a bad idea to Spy check him.