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

Annotations already declare readOnly, idempotent and non-destructive, so the safety profile is covered. The description adds genuinely useful behavior beyond that: the pricing model (first mug full price, subsequent mugs discounted, discount applies across different designs), that shipping may be free, and that it mirrors checkout maths before promo codes. It stops short of describing rounding, currency handling or rate behavior, so it is not a 5.

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 dense sentence that front-loads the core purpose and then lists the output components; nothing is wasted. It is slightly run-on, which keeps it from being a model of structure, but the information density is high.

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 one parameter, full annotations, and no output schema, the description supplies what an agent needs: what is computed, in what currency, and which figures are returned. The only minor gap is that promo codes and any limits on the quantity/order context are only implicitly addressed.

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's bounds (1-500) and meaning ('Number of mugs in one order') are fully documented there. The description's mention of discounts across different designs is a pricing rule rather than added meaning about the quantity argument itself, so this is correctly at the baseline where the schema does the work.

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 computation (exact price for a given number of mugs) and states the currency (EUR), which unambiguously separates it from every lookup-oriented sibling such as get_shop_overview or get_delivery_estimate. It also enumerates the components of the result (unit pricing, shipping, total), so the agent knows what the tool produces.

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?

Usage is implied by the resource: call it when you need a price for a quantity of mugs. However, there is no explicit statement of when to prefer this over a sibling, nor any exclusion (e.g., promo-code pricing is out of scope, which is only hinted at by 'before any promo code'). The context is inferable but not spelled out.

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