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

Annotations already declare readOnlyHint, idempotentHint, and non-destructive, so safety is covered. The description adds real behavioral context beyond that: it discloses that the tool surfaces the limits of what public packaging evidence can prove, which is a semantic caveat an agent could not infer from the schema or annotations.

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?

Two sentences, zero filler. The first sentence identifies the payload (evidence labels + their limits) and the second gives the usage trigger, both front-loaded with no redundancy.

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?

For a read-only policy/explanation tool with one fully documented optional parameter and no output schema, the description covers what the agent needs: what it returns conceptually and when to call it. A brief note on the response language behavior or shape would close the remaining gap, but nothing essential is missing.

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?

Only one optional parameter (locale) exists and the schema documents it fully at 100% coverage, including the enum values and default. The description adds nothing about the locale parameter, but the schema already carries the full burden, 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 description names a specific action (explain) and enumerates the exact content returned: the Observed/Derived/Inferred/Unknown evidence labels and the limits of public packaging evidence. It is not a tautology of the name. It doesn't need to distinguish itself from list_directories or search_brands since those are unrelated CRUD/search operations, but it also doesn't explicitly say so.

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 gives explicit invocation timing: 'Call this before drawing conclusions about a brand's suppliers, materials, or buying intent.' That is a clear when-to-use trigger tied to downstream tasks. It stops short of naming alternatives or a when-not-to-use condition, which is minor given this is a singleton policy tool.

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