Run, pause and stop the simulation

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

Annotations declare openWorldHint=true and destructiveHint=false (though the tool stops/discards state). The description goes further: it states that play adds a second connected session hosting the game, that the call is non-blocking and reports the reached state, that stop discards changes exactly like pressing Stop, and that EndTest's value surfaces as lastResult. This is rich behavioral detail beyond the annotation flags, though it doesn't enumerate failure modes or edge cases (e.g., what happens if stop is called before any test).

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

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

Dense but every sentence earns its place: op semantics up front, then async behavior, then studioId routing, then stop/EndTest contractholics. No filler, well-organized into scannable paragraphs.

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

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

Comprehensive for a control tool. It explains non-blocking behavior, side effects of stopping, how to discover the right studio, and the return-value semantics. Minor gaps: no failure modes or preconditions (e.g., must be in edit mode for play), and no mention of auth, but the description is unusually complete for the domain.

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

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

Even though the schema already documents all 4 parameters at 100% coverage, the description adds substantial semantic value: it explains the async nature of the reply ('returns the state reached'), how args is consumed inside the test, and the meaning of the state operation as a pure reporter. That goes beyond the schema's enumerations and helps an agent avoid misusing op as a blocking call.

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

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

The description uses specific verbs ('starts', 'stops', 'reports') tied to a clear resource ('playtests') and enumerates the five op values with distinct one-line meanings. It distinguishes the modes play/run/multiplayer and singles out state as read-only, so an agent can tell them apart 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.

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

Explicitly explains when to use play vs run vs multiplayer, warns that stop is the only way to end a test besides EndTest, and instructs calling list_studios after starting so console/performance/execute_luau target the playtest's studioId. This is actionable routing guidance with no ambiguity.

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