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Creep
A programmable unit built from body parts such as MOVE, WORK, CARRY, ATTACK, and HEAL.
SCREEPS GLOSSARY
Core terms without the detour
Use these short definitions while reading the API, debugging Console output, or following the beginner roadmap.
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Spawn
A player-owned structure that creates Creeps when the room has enough available Energy.
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Tick
One simulation step. Your loop runs again on each tick, so multi-step behavior must preserve state.
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Game loop
The exported function that reads the current world state and issues actions for the current tick.
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Memory
Persistent JSON-compatible data used to carry decisions and state across ticks.
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Controller
The room object that determines ownership, reservation, and Room Controller Level.
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RCL
Room Controller Level. It controls structure limits and unlocks room capabilities.
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GCL
Global Control Level. It limits how many rooms an account can control.
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CPU limit
The normal CPU allowance available to your code over time.
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CPU bucket
Stored CPU credit that rises when usage is low and can support temporary bursts.
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Store
A capacity interface used by Creeps and structures to hold Energy and other resources.
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Fatigue
Movement delay accumulated by a Creep. Active MOVE parts reduce fatigue each tick.
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Room visibility
Access to live room objects. A room outside current vision cannot be read from Game.rooms.
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Return code
A numeric result from a Screeps method that explains whether the action was accepted or why it failed.
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Construction Site
A planned structure location that requires build progress before the structure exists.
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PathFinder
The path search system used for custom movement costs, obstacles, and multi-room routing.
Need a numeric result?
Open the English error-code reference when a method returns 0, -2, -6, -8, -9, or another Screeps constant.
Open error codes →