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

Annotations already declare readOnly=true, idempotent=true, destructive=false, so the safety profile is covered. The description adds genuine value beyond them: it discloses the underlying data source (advertise pages) and the precise metric (median price for the main sponsor slot of a single issue).

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: the first front-loads the usage trigger, the second defines the return. No filler, nothing redundant.

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 and full annotation coverage, the description does not need to explain return values, and it correctly focuses on trigger and metric. Nothing an agent needs to invoke this correctly 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?

Schema description coverage is 100% and the single parameter is documented in the schema. The description adds only the notion that subscribers map to a 'size band,' which is marginal clarification over the schema; baseline 3 fits.

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 states a clear verb and resource: it returns the median listed sponsorship price. It also scopes the result ('main sponsor slot of one issue, by list size') and names the data source ('their own advertise pages'). It does not explicitly distinguish itself from the siblings, but the purpose is distinct enough that confusion is unlikely.

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 trigger phrasing ('Use this when someone asks how much to charge for a newsletter sponsorship or what newsletters charge for an ad'), which is strong context. It stops short of naming when-not-to-use or pointing to a sibling as an alternative, so it is not a full 5.

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