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

Annotations already declare readOnly, idempotent, non-destructive and closed-world, so the safety profile is covered. The description adds genuinely new behavioral context — the fallback that anything unstated is returned as 'on request' — which no structured field conveys. It does not mention auth or rate limits, but those are secondary for a read.

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, front-loaded with the core action and resource, then the conditional variant. Every clause carries information; nothing is repeated from the title or schema.

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 must convey the return shape, and it does so concretely (category, availability markets, delivery methods, plans, store prices, plus the 'on request' fallback). For a two-parameter read tool this is sufficient to call 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 coverage is 100%, so the baseline is 3, and the description earns a bump by clarifying what `market` actually unlocks (plans and Fleek's public store prices in that country) — information the schema's 'for its store prices' only partially covers. It adds no format caveats for `brand` beyond what the schema already says.

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 ('Look up one brand in Fleek's catalogue') and enumerates exactly what is returned: category, markets, delivery channels. The singular 'one brand' implicitly contrasts with the sibling `search_catalogue`, so an agent can pick between them without opening either schema.

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 description implies usage by explaining the conditional effect of a country ('With a country, also its plans and ... public store prices there'), which tells the agent when to supply the optional param. However, it never names an alternative (`search_catalogue`, `shortlist_for_programme`) or states when not to use this tool, leaving routing to inference.

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