task.wait(n?): yields for about n seconds (default one frame) and returns elapsed time.
task.spawn(f, ...): schedules f to run asynchronously.
task.defer(f, ...): defers f until after the current event cycle.
task.cancel(thread): cancels a thread returned by task.spawn/task.defer.

For parallel code, task.desynchronize() and task.synchronize() move the current thread between the parallel and serial phases.

Services by purpose

Container / hierarchy services (visible in Explorer, part of the DataModel):

Workspace (3D content)
Lighting (environment, atmosphere, post effects)
ReplicatedStorage / ReplicatedFirst (shared code & assets)
ServerScriptService (server-only logic)
StarterGui / StarterPlayer / StarterPack (templates cloned to players)
Players, Teams, SoundService, etc.

Core runtime & scripting services:

RunService: Heartbeat fires after physics on both sides; PreSimulation fires before physics on both sides; PreRender is client-only and fires before rendering.
TweenService (see animation skill)
CollectionService (tags)
ContextActionService, UserInputService, GuiService
ContentProvider (preloading)

Cloud / persistence / cross-server:

DataStoreService, MemoryStoreService, MessagingService (see roblox-datastores skill)

Monetization:

MarketplaceService (gamepasses, dev products; see dedicated skill)
BadgeService, etc.

Other high-value ones: TeleportService, AnalyticsService, HttpService (outbound only + JSONEncode/Decode), PathfindingService, etc.

Discover services with game:GetService (known services) or game:FindService (optional). Avoid using game:GetChildren() for service discovery. Not every DataModel child is a service, and services can be lazily created. Acquire each service once per script/module.

Instance creation best practice

Configure an instance before parenting it to avoid redundant replication and extra changed events:

local part = Instance.new("Part")
part.Anchored = true
part.Size = Vector3.new(4, 1, 2)
part.Position = Vector3.new(0, 10, 0)
part.Parent = workspace

Set Parent last; do not use the Instance.new("Part", parent) two-argument form.

Types and serialization

Read luau-data-types-and-serialization.md before designing persisted values or debugging serialization. DataStores, JSON, and remotes have different supported types. A successful JSONEncode is a useful check, but it does not prove that a value meets every DataStore constraint.

Type checking

Gradual and opt-in. Use --!strict at the top of a file (it is file-level) or a .luaurc project configuration for project-wide type checking. Add annotations (local x: number, function signatures) for large modules. Inference does a lot of the work. Catches bugs at edit time with zero runtime cost.

Script locations and execution contexts

ServerScriptService + Script (RunContext.Server) → server only, with access to server APIs such as DataStores.
ReplicatedStorage → stores shared ModuleScripts/assets. A Script here only runs if its RunContext is set to Client or Server; use ModuleScripts for shared logic.
StarterGui + LocalScript → per-player client only (inside the cloned PlayerGui).
ReplicatedFirst + LocalScript → very early client execution (loading screens).
Actor + Script with RunContext.Client/Server → can run Parallel Luau when the code calls task.desynchronize() or uses ConnectParallel(). The Actor must be parented to the DataModel and the Script must have an explicit RunContext; placing a Script inside an Actor alone does not parallelize it. require() can be called from parallel contexts only when the module itself is parallel-safe; most engine APIs and many modules are not.
Tools have special execution contexts. HopperBins are deprecated/legacy and should not be used for new work.

Modern Roblox uses BaseScript.RunContext (Legacy, Server, Client, Plugin). Legacy exists only for backward compatibility and is location-dependent; prefer explicit Server or Client for new code. RunContext is set in Studio's Properties window and is read-only at runtime.

Always branch runtime authority with RunService:IsServer() and IsClient(). IsStudio() detects the environment (Studio vs. live), not runtime context, so use it only for test/development guards.

Never put datastore writes, economy, or authoritative gameplay logic anywhere a client can influence it directly.

"Files" and data in Luau/Roblox

Inside a running experience there is no direct filesystem access (security). You cannot open arbitrary files or write player-visible logs.

What you have instead:

DataStores / MemoryStores for persistent or temporary "save data".
ModuleScripts for reusable code (require works like a cached module system: a ModuleScript runs once and returns the same value on subsequent requires).
HttpService:JSONEncode/Decode + web calls for external data exchange.
In Studio: plugins have limited file APIs, and external tools (Rojo, Script Sync) can sync code from the filesystem, but experience scripts never have arbitrary filesystem access.

For complex data you often serialize tables to JSON strings for storage or transmission.

Additional runtime considerations

Attributes: use :SetAttribute/GetAttribute for lightweight per-instance data; prefer them over legacy Value objects.
Random: use the Random class (Random.new(seed)) for deterministic or independent random streams instead of global math.randomseed.
StreamingEnabled: on the client, instances can stream in/out; always use WaitForChild/Instance.StreamingMode defensively and avoid hard references to far-away parts.
table utilities: table.create(n, value), table.find(t, value), table.clone(t), and table.freeze(t)/table.isfrozen(t) are the modern helpers.
BaseScript.Enabled: disables/enables a script without deleting it.
ModuleScript caching: require executes a ModuleScript once per environment and caches the returned value.
Sequence / physical types: NumberSequence, ColorSequence, and PhysicalProperties are common Roblox datatypes for particles, beams, and part materials.

Architecture foundations

Server authority is the default safe posture.
Replication is selective and streaming-aware.
Use ReplicatedStorage for shared modules/assets, ServerScriptService for server logic, StarterGui for client UI entry points.
CollectionService tags + Attributes for lightweight grouping and data without heavy Instance hierarchies.
Parallel Luau + Actors when you need CPU-bound work off the main thread.

Scripts

scripts/ServiceHelper.lua: small utilities for safely acquiring services and requiring modules with timeouts.

Reference index

luau-data-types-and-serialization.md: Choose data types or diagnose serialization failures.
script-locations-contexts-and-architecture.md: Decide where scripts run or debug loading and replication.
services-catalog-and-usage.md: Choose a service or load services and modules.

roblox-core

roblox-core

Script initialization

Modern task library