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

Annotations only declare the safety profile (not read-only, open-world, not idempotent, not destructive); the description adds substantive behavior beyond that — what entering PLAY mode actually does to scripts, physics, and write locking, that it returns the resulting run-state, and that calls are refused under a named diagnostic condition. The refusal path and its error-surfacing behavior are unusual and genuinely useful disclosures that annotations cannot convey.

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?

Three front-loaded sentences with no filler: the action and its effects lead, the return value follows, and the failure condition closes. Each sentence carries distinct information an agent needs.

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?

With annotations covering safety and the schema covering the one parameter, the description supplies the remaining essentials: effects, return shape, and refusal semantics. It stops short of describing what the run-state contains or how re-entry while already in PLAY behaves, but no output schema exists that would otherwise carry that burden.

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?

There is a single optional parameter (`as`) and the schema description already documents it at full coverage, including naming conventions and multiplicity semantics. The description says nothing about it, so per the high-coverage baseline it neither compensates nor detracts.

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 names a concrete action and target state ("Flip the connected world into PLAY mode") and enumerates the observable consequences — scripts tick, physics simulates, `/zero` writes lock — which is far more specific than a bare mode switch. It does not explicitly name its obvious counterpart `pause`, so differentiation from the sibling is left to inference from the mode name rather than stated.

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?

It states a clear precondition and the prescribed remedy: refused while error-severity diagnostics exist under `/zero/source`, and the agent should fix those rather than work around the refusal. What's missing is the symmetric guidance — when to call `pause` instead, or what happens if the world is already in PLAY, so the alternative route is never spelled out.

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