List nil-parented (hidden) instances

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

Annotations already declare readOnly/idempotent/non-destructive, and the description goes well beyond them: it discloses the return shape (total count, byClass breakdown over ALL nil instances, capped samples), the getnilinstances dependency, graceful degradation with a clear error, cost phase, and active-client requirement. This is rich behavioral context an agent cannot get from 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.

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

It is front-loaded with the purpose and the key scoping/hiding-spot rationale, and the return-shape summary is efficient. It loses a little to redundancy: the signature duplicates the schema and 'Safety: read-only' / 'idempotency=read-only' restate the annotations.

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 no output schema, the description itself explains the returned structure (total, byClass, samples with class/name/path), the dependency and fallback behavior, and the operational requirements, so an agent has everything needed to invoke and interpret it correctly.

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?

Schema description coverage is 100%, so both parameters are already fully documented, including the note that byClass/total ignore the limit. The description's 'Signature: { limit: any?, threadContext: number? }' merely restates the schema and adds no new semantic detail, so the baseline of 3 applies.

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 definition gives a precise verb+resource ('Enumerate instances whose Parent is nil') and defines the exact condition that makes an instance nil-parented, so an agent can distinguish this from generic hidden-instance scans without opening the schema. The added explanation of why nil parenting is a hiding spot makes the scope unambiguous.

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 supplies clear context for when this is valuable ('classic hiding spot', unreachable from the game tree, invisible to Explorer/descendant scans), which is strong usage framing. However, it never explicitly contrasts this with alternatives in the sibling set such as find-detached-instances, find-hidden-instances, or find-hidden-guis, and gives no exclusions.

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