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Roblox Studio MCP

What a class can do

api
Read-onlyIdempotent

Discover Roblox class members by listing properties, methods, and events from the running engine. Check signatures and find class names to write accurate Luau code.

Instructions

Lists the properties, methods and events of any Roblox class, read from the engine that is running.

Use it before writing Luau against a class you are not certain of. Guessing a method name costs a runtime error and a round trip; this costs one call and is never out of date, because the answer comes from the running binary rather than from a published dump or from training data. That matters most for exactly the classes worth checking — new ones, and ones that changed recently.

Members come back as signatures rather than bare names — AddAccessory(accessory: Instance), HoldDuration: number — because a name tells you something exists and a signature tells you how to call it, which is the actual question.

describe takes a class name and gives the members it declares itself, counting the inherited ones separately. classes searches class names, which is how to find one whose exact spelling you do not have.

Deprecated members are never listed, only counted — Instance has eight, including clone, remove and getChildren. They still run, so picking one from a list gives you working code and a deprecation warning in the user's output.

This is not the same as inspect. inspect reads the values on an instance that exists; this reads the shape of a class whether or not anything in the place is one — which is what you need when deciding what to create in the first place.

Input Schema

TableJSON Schema
NameRequiredDescriptionDefault
opNo'describe' details one class, 'classes' searches class names.describe
includeNodescribe only: which member kinds to return. Defaults to all three; narrow it when you only need one and the class is large.
containsNoclasses only: substring to match, case-insensitive, e.g. "constraint" or "gui". Omit to list everything.
studioIdNoTarget Studio; omit for the active one.
classNameNodescribe only: the class, e.g. "TweenService", "ProximityPrompt", "Humanoid". Case-sensitive.
inheritedNodescribe only: include members inherited from Instance and Object. Off by default because they swamp the answer — ProximityPrompt has 2 methods of its own and 42 inherited, and the two you want are not the ones you already know. The inherited count is reported either way.
Behavior5/5

Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?

Beyond the readOnlyHint and idempotentHint annotations, the description discloses several crucial behaviors: results come 'from the running binary rather than from a published dump', members return as signatures, deprecated members are 'never listed, only counted', and the `describe` vs `classes` operational split. These are non-obvious traits that directly affect how the tool should be called and interpreted, adding real value over the annotations alone.

Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.

Conciseness5/5

Is the description appropriately sized, front-loaded, and free of redundancy?

The description is long but every paragraph earns its place. The first sentence states the core purpose, and subsequent paragraphs each cover a single behavioral aspect—freshness, return format, deprecation handling, and relationship to `inspect`—without redundancy. The ProximityPrompt example is illustrative, not filler.

Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.

Completeness5/5

Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?

For a 6-parameter tool with no output schema, the description fully covers what an agent needs to know: the return shape (signatures), default behaviors, deprecation semantics, and how to discover class names. There are no missing pieces that would leave an agent guessing how to invoke this correctly.

Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.

Parameters5/5

Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?

Even though the schema covers 100% of parameters, the description adds substantial semantic context: it clarifies the two enum values of `op`, explains the `inherited` parameter's default and trade-off with a concrete example ('ProximityPrompt has 2 methods of its own and 42 inherited'), and specifies case-sensitivity of `className`. This goes well beyond what the JSON schema alone provides.

Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.

Purpose5/5

Does the description clearly state what the tool does and how it differs from similar tools?

The description opens with a specific verb+resource: 'Lists the properties, methods and events of any Roblox class', and later explicitly differentiates from sibling `inspect` ('This is not the same as `inspect`. `inspect` reads the values on an instance...'). An agent can immediately tell what this tool does and how it differs from closely related tools.

Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.

Usage Guidelines5/5

Does the description explain when to use this tool, when not to, or what alternatives exist?

Explicit when-to-use guidance is present: 'Use it before writing Luau against a class you are not certain of.' It also names when not to use it by contrasting with `inspect` ('this reads the shape of a class whether or not anything in the place is one'). This leaves no ambiguity for tool selection.

Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.

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