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

Annotations already declare readOnly, idempotent, non-destructive, closed-world behavior, so the safety profile is covered. The description adds genuinely useful context beyond that: the response is conditional, returning ranking metrics only when the product is ranked and otherwise the reason it isn't. No auth or rate-limit notes, but none are needed for a read-only lookup.

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?

A single front-loaded sentence with no filler, and the conditional return behavior is packed efficiently into a parenthetical. It is dense but readable; a slight restructuring could have separated the return-value clause from the identity clause.

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 carries the burden of describing returns and does so, including the important non-ranked branch. The region parameter's effect on results is left entirely to the schema, which is a minor gap for a two-parameter tool.

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%, including the slug regex and the region enum-like values, so the schema does the heavy lifting. The description adds no extra meaning about how region affects results or what happens with an unknown slug; baseline 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 verb-resource pair ('One product by its LabelTruth slug') and enumerates the returned fields (shelf price, store, euro per 1000 mg), which makes it clearly distinct from the list-oriented siblings. It stops short of explicitly differentiating itself from cheapest_in_form or list_forms, so a 5 isn't warranted.

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?

There is no when-to-use or when-not-to-use guidance, and no alternative tool is named. The only implicit signal is that a slug is required, which the schema already states; an agent must infer the use case (look up a known product vs. search for a cheap one) on its own.

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