PvP build order and strategy: Protoss vs Protoss

Checklist: do this

One gateway, core, second gateway; dragoons with range by 3:30 hold the ramp against anything.
Robotics facility by 4:30: an observer against dark templar, a reaver for the first fight.
Nexus at the natural around 5:30 behind dragoons and the reaver; a shield battery at the ramp helps.
Three or four gateways on two bases; ground weapons +1 from a forge by 7:00.
Citadel for zealot speed and templar archives later; storms decide big dragoon fights.
Third nexus around 9:00 behind a reaver and a shield battery; arbiters or carriers only in long games.
Scout with the probe at 2:00 and again at 4:00: a second gateway, a citadel or a robotics facility each change one thing.
Never fight up a ramp; hold yours, attack theirs only with a reaver and a numbers edge.

Why it works

Both players have the same units, so the game is decided by the first two choices: how many gateways before the core, and robotics or templar archives after it. Dragoons with range hold everything early; dark templar win instantly against a player with no observer; a reaver behind dragoons wins the mid-game fight. Play safe against the coin flips, then out-produce.

If you remember one sentenceTwo gateways of dragoons with range, a robotics facility for the observer and a reaver, then expand and out-gateway them.

The build

Supply8 Time0:55 Pylon Never blocked at 8.
Supply10 Time1:25 Gateway The first zealot if the scout sees two gateways.
Supply12 Time1:50 Assimilator Core gas.
Supply14 Time2:25 Cybernetics Core Dragoons; range as soon as it finishes.
Supply16 Time3:00 Second Gateway, Dragoon Two gateways of dragoons hold the ramp.
Supply19 Time3:20 Singularity Charge Range wins dragoon versus dragoon.
Supply24 Time4:30 Robotics Facility Observer against dark templar; reaver for the fight.
Supply28 Time5:10 Observatory, Robotics Support Bay The observer first, then the reaver.
Supply32 Time5:40 Nexus at the natural, Shield Battery Expand behind dragoons, a reaver and a battery.
Supply38 Time6:30 Third Gateway, Forge Ground weapons +1 by 8:30.
Supply48 Time7:30 Fourth Gateway, Citadel of Adun Zealot speed makes zealots part of the fight again.
Supply60 Time9:00 Third Nexus, Templar Archives Storms for the late dragoon wars.

Research, in this order

Singularity Charge at the Cybernetics Core
The first research of the game; range wins every dragoon fight.
Scarab Damage at the Robotics Support Bay
A reaver that kills dragoons in two scarabs.
Ground Weapons +1 at the Forge
Dragoon fights are decided by upgrades once numbers are even.
Leg Enhancements at the Citadel of Adun
Speed zealots close on dragoons and reavers.
Gravitic Boosters at the Observatory
Observers keep up and survive.
Psionic Storm at the Templar Archives
Storms on a dragoon ball end the fight.

The army, stage by stage

Opening
Dragoon
Four to six dragoons with range at the ramp.
Robotics
DragoonObserverReaver
The observer with the army; the reaver behind the dragoons.
Two bases
DragoonZealotReaverObserver
Speed zealots in front once leg enhancements finish.
Late game
DragoonZealotHigh TemplarReaver
Storms and archons; carriers on wide maps in very long games.

If you scout…

Two gateways before a core, zealots at 2:30

When The probe scout

Do One zealot, then dragoons; probes on the ramp; core on time.

Why Zealot pressure fails against a held ramp and leaves them without dragoons.

A citadel of Adun before a robotics facility

When 4:00 to 5:00

Do Observer first from the robotics facility, a cannon at the ramp and one at the mineral line.

Why Dark templar at 6:00 end the game without detection; with it they are two dead units.

A robotics facility before yours

When 4:00 to 5:00

Do Your robotics on time, dragoons spread, a shield battery; do not attack into their reaver.

Why The first reaver wins the first fight for whoever has it; hold until yours exists.

A fast nexus

When 4:00 to 5:00

Do Attack with six dragoons and a reaver before their gateways catch up, or expand at once.

Why A fast expansion has few units at 6:00; a reaver push punishes it.

A stargate

When 6:00 onward

Do Dragoons in numbers, a cannon at each mineral line, keep the observer alive.

Why Corsair-reaver or carriers lose to massed dragoons that see the shuttle.

Counters

They have	You answer with
Dragoons	Range, upgrades, a reaver, storms Even dragoons trade; range and a reaver tip it.
Zealots	Dragoons kiting up a ramp, a reaver Zealots cannot reach dragoons that retreat.
Dark Templar	Observers, cannons Detection turns them into slow zealots.
Reavers	Dragoons on the shuttle, spread units, your own reaver A reaver without its shuttle is stranded; spread units waste scarabs.
High Templar	Spread dragoons, zealots on the templar Storm needs a clump.
Carriers	Dragoons in numbers Massed dragoons with upgrades kill carriers faster than they build.

The mistakes that lose this matchup

No observer
The sign A base dead to two dark templar at 6:00.
The fix Robotics facility at 4:30, observatory next, an observer by 6:00 every game.
Fighting up a ramp
The sign Dragoons lost with nothing killed.
The fix Hold yours; attack theirs with a reaver and more dragoons.
Late range
The sign Losing even dragoon fights.
The fix Singularity charge the moment the core finishes.
Expanding with no reaver
The sign A natural lost to six dragoons.
The fix Nexus behind the first reaver and a shield battery.

By level

Newcomer

Gateway, core, second gateway, dragoons with range. Robotics facility, observer, reaver. Then expand and keep every gateway producing. Hold your ramp; do not attack up theirs.

Learner

The build within thirty seconds; scout at 2:00 and 4:00 and pick from the forks; a reaver by 6:30 with scarab damage; +1 weapons by 8:30; a third base at 9:00 behind a battery.

Competitor

Dragoon micro on ramps, reaver-shuttle control, observer positioning against dark templar and against their observer, storm timing in dragoon wars, and the decision to go templar or carriers from the map and the opponent's gas.