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Roblox Executor MCP Server

by okenjioxx
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TypeScript
Local

Append content to a file in the executor workspace (UNC appendfile)

append-file
Destructive

Append text to a file in the executor's workspace, preserving existing content and creating the file if it does not exist yet.

Instructions

Append content to the end of a file in the executor's workspace folder, creating the file first if it does not exist. Existing contents are preserved (unlike write-file, which overwrites). NOTE: this is executor-side file I/O — the connector runs INSIDE the executor, so the path is relative to the executor's workspace directory on the host machine, NOT the Roblox game. Requires the UNC function appendfile(path, content). The call is type-guarded and pcall-wrapped: if appendfile is missing you get { error = 'appendfile is not available in this executor.' }, and any failure returns { error = }. Returns { path, ok = true } or { error }. Signature: { path: string, content: string, threadContext: number?, timeoutMs: number? }. Phase: act; cost=medium; idempotency=contextual-write. Requires: active-client, resolved-target, explicit-mutation-approval. Capabilities: executor filesystem. Produces: operation-receipt. Verify with: file-exists. Safety: MUTATING; writes executor workspace filesystem. On failure: inspect tool-schema for exact fields, defaults, constraints, and an invocation example.

Input Schema

TableJSON Schema
NameRequiredDescriptionDefault
pathYesPath to the file within the executor workspace folder, e.g. 'logs/session.txt'. Created if missing.
contentYesThe text content to append to the end of the file.
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

A4.6/5.0
Behavior5/5

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

Annotations already flag destructiveHint=true and non-idempotent, and the description adds substantial context beyond them: type-guarded/pcall-wrapped behavior, exact error shapes ({ error = 'appendfile is not available...' }, { error = <message> }), the required UNC function, prerequisites (active-client, resolved-target, explicit-mutation-approval), and verification via file-exists. This is unusually rich 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-loaded with purpose and the key write-file contrast in the first two sentences, which is where it matters most. It is long and carries some metadata (phase/cost/idempotency labels) that borders on noise, but nearly every clause contributes decision-relevant information.

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?

With no output schema, the description fully compensates by documenting return values ({ path, ok = true } or { error }), error conditions, prerequisites, and a verification step. Nothing an agent needs to invoke this mutation correctly is missing.

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

Parameters3/5

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

Schema description coverage is 100%, so the schema already documents all four parameters. The description restates the signature ({ path, content, threadContext?, timeoutMs? }) but adds no format or constraint detail beyond what the schema provides. Baseline 3 is appropriate.

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+resource (append content to the end of a file in the executor's workspace folder) and explicitly differentiates from the sibling write-file by noting write-file overwrites while this preserves contents. An agent can distinguish it without opening either schema.

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?

Explains exactly when to use it (append to end, create if missing, preserve existing content) and names the alternative (write-file) with the condition that selects it. Also clarifies the executor-side vs Roblox-game scope, removing the most likely misuse.

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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