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

No annotations, so the description carries the full load, and it discloses real behavior: the 8 priced regions return local currency, other countries return USD/default with pricingCountry=US fallback metadata, packs stack on any paid plan, and Free users are excluded. Gaps remain on whether prices are tax-inclusive or how many packs are returned.

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?

Lead sentence identifies the resource and pack tiers, then pricing behavior, then eligibility, then the when-to-use trigger is front of the third sentence. It is dense but each sentence adds information; only the id enumeration mildly duplicates the 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 and no annotations, the description does the work of explaining pricing-region fallback and purchase eligibility, which an agent needs to answer correctly. A brief note on the returned fields (pack name, credits, currency, price) would close the remaining 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?

Schema coverage is 100% and both params are enums fully described in the schema, so the baseline applies. The description repeats the id values (boost/power/mega/ultra) and restates the country fallback rule, adding no syntax or semantics 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?

The first sentence names the exact resource (HelloBooks AI credit packs), clarifies they are one-time pay-as-you-go top-ups, and enumerates the four SKUs with their credit sizes. This keeps it distinct from list_plans, which covers subscriptions, and the 'stack on any paid plan' line reinforces that distinction.

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 explicitly says when to call: a user asking how to buy more AI credits or top up after exhausting a plan allowance. It also gives a negative case (Free users cannot buy packs and should upgrade). It never names list_plans or list_features as alternatives, so routing versus siblings is implied rather than explicit.

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