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

Annotations cover read-only and open-world behavior, but the description adds meaningful non-schema context: the call is anonymous, service-agnostic, and resolves the labeler's endpoint from its DID document rather than a hardcoded aggregator. It does not discuss rate limits or error behaviors, so not a 5.

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?

Purpose and example are front-loaded in the first sentence, with the subject/labeler semantics in the second. Dense but every clause earns its place; the method-name parenthetical is slightly redundant with the title field being null.

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 an output schema present, return values need no explanation, and the description covers purpose, subject/labeler input semantics, and pagination implication via the cursor mention. It leaves out any failure modes (unknown labeler DID, invalid at:// URI), which keeps it short of complete.

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 coverage is 100%, so the descriptions of limit, cursor, labeler and subject are already in the schema. The prose largely restates those (subject as DID/handle vs at:// URI, labeler as handle/DID) and adds only a concrete example value for labeler, so it stays at the baseline.

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?

States a specific verb and resource ('what moderation labels a labeler has applied to a subject') and immediately names the ATProto method, so the agent knows exactly what is retrieved. It is clearly distinguishable from sibling list_labelers, which enumerates labelers rather than querying labels they applied.

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?

The quoted example question ('has @alice or this post been labeled spam/nsfw/hidden by labeler X?') gives a concrete usage context, effectively telling the agent when this tool applies. It does not, however, name an alternative tool or state when not to use it.

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