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Roblox Executor MCP Server

Roblox Executor MCP Server

by okenjioxx
OverviewSchemaSourceRelated ServersDiscussionsAdmin
TypeScript
Local

Override a Roblox FastFlag value (sUNC setfflag)

set-fast-flag
Destructive

Overrides a Roblox engine FastFlag for the running client via setfflag(name, value). Changes engine behavior at runtime; may destabilize the client if an invalid value is set.

Instructions

WRITES CLIENT STATE — overrides a Roblox engine FastFlag for the running client via setfflag(name, value). The value is supplied as a string and coerced by the executor to the flag's native type (bool/int/string). This changes engine behavior at runtime and can destabilize the client if a flag is set to an invalid value. Requires setfflag. The call is type-guarded and pcall-wrapped: if setfflag is missing you get { error = 'setfflag is not available in this executor.' }. Returns { name, value, ok } or { error }. Signature: { name: string, value: string, threadContext: number?, timeoutMs: number? }. Phase: act; cost=medium; idempotency=idempotent-write. Requires: active-client, explicit-mutation-approval. Produces: operation-receipt. Verify with: assert-state. Safety: MUTATING; writes live game/client state. On failure: inspect tool-schema for exact fields, defaults, constraints, and an invocation example.

Tool call template

Replace each placeholder with a value matching the input schema. Only required parameters are included; add optional parameters as needed.

{
  "id": 1,
  "jsonrpc": "2.0",
  "method": "tools/call",
  "params": {
    "arguments": {
      "name": "<name>",
      "value": "<value>"
    },
    "name": "set-fast-flag"
  }
}

Input Schema

NameRequiredDescriptionDefault
nameYesThe FastFlag name to override, e.g. 'DFIntTaskSchedulerTargetFps'.
valueYesThe new value as a string (e.g. '120', 'true', or a text value).
timeoutMsNoOptional per-call deadline in milliseconds; omit it to use the tool or server default.
threadContextNoOptional Roblox thread identity for this call; omit it to use the server default.

Schema Changelog

Changes observed during successful MCP inspections.

  1. First observedv2.0.0-spies.2

TDQS

A4.1/5.0
Behavior3/5

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

The description is rich beyond the annotations: value coercion to the flag's native type, pcall/type-guard wrapping, the exact error shape, and the { name, value, ok } return shape. However, it labels the operation 'idempotency=idempotent-write' while the annotations declare idempotentHint=false, a genuine conflict that undercuts the otherwise strong behavioral disclosure.

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

Conciseness4/5

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

Front-loads the critical 'WRITES CLIENT STATE' warning, then error/return behavior, then signature. It is long and somewhat repetitive ('Requires setfflag' is restated, trailing 'On failure: inspect tool-schema' is boilerplate), but each block is useful.

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

Completeness4/5

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

With no output schema, the description supplies the return shape and error envelope, and there are no nested objects or enums to cover. It is nearly complete for a mutating 4-param tool; the only slip is the inconsistent idempotency claim.

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

Parameters4/5

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

Schema coverage is 100% and documents each parameter, so the baseline is 3. The description adds real meaning: the value is a string coerced by the executor to the flag's native type (bool/int/string), and it repeats the full signature with optionality, exceeding the schema alone.

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?

States a specific verb (overrides) and resource (a Roblox engine FastFlag for the running client) with the underlying call setfflag(name, value). It is clearly distinguishable from siblings like get-fast-flag and set-fps-cap. An agent knows exactly what this does without opening the schema.

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

Usage Guidelines4/5

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

Provides clear invocation context: 'Phase: act', 'Requires: active-client, explicit-mutation-approval', 'Requires setfflag', and 'Verify with: assert-state'. It does not explicitly name alternatives or when-not-to-use (e.g., 'use get-fast-flag to read'), so it stops short of a 5.

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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