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

Annotations already carry readOnlyHint/idempotentHint/non-destructive/closed-world, so the safety profile is covered. The description adds real behavioral context beyond that: results are conditional on authentication ('With an API key it also lists the user's own listings and which of them can be advertised or are already sponsored'), which the agent could not infer from the 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 tight sentences with no filler; the identity of the data set is front-loaded and the workflow hint comes last. Every clause earns its place.

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 name the fields (price, billing, duration) and the auth-conditional extra data. It omits any note on pagination, ordering, or empty-result behavior, which for a list tool is a minor but real gap.

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?

There are zero parameters, so the baseline is 4 by rule; the schema is empty and additionalProperties=false. The description's mention of an API key explains an implicit ambient input (auth) that changes the response, adding a bit of value even without parameters.

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 the resource precisely ('Sponsored-placement advertising packages') plus the attributes returned (price, billing, duration). The verb is implied by the name/title rather than stated, and it doesn't explicitly contrast with siblings like list_plans or get_my_listings, which keeps it just short of a 5.

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?

"Use before prepare_advertising" gives an explicit ordering and names the sibling it precedes, so the agent knows the workflow context. It does not state when NOT to use it or what alternative to prefer if the agent only wants the user's own listings, so it falls short of 5.

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