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

Annotations already declare readOnlyHint=true, openWorldHint=true, idempotentHint=false and destructiveHint=false. The description adds genuinely new behavioral facts: the data comes from the official HN API, each call is billed ($0.01, first 25 free, failed calls free), and repeats are not free because of per-call charging — which operationalizes the idempotentHint=false in practical terms. It omits freshness/caching behavior and rate limits, so it is strong but not exhaustive.

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?

The core purpose and returned fields are front-loaded in the first clause, followed by the usage cue and example. The pricing sentence is dense with payment-channel detail (x402 USDC, card key /credits) that is useful but slightly crowds the definition.

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 optional parameter, no output schema, and annotations covering safety, the description fills the remaining gaps: it lists the return fields, names the upstream source, and discloses the cost model. An agent has everything needed to decide to call it and to set count 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 description coverage is 100% and the single parameter is already documented as "How many (1-20, default 10)". The description only adds an example value (count=5), not new semantics such as how out-of-range values are handled. Baseline 3 is appropriate when the schema carries the meaning.

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?

"Current top stories on Hacker News" names a specific resource and scope, and the description enumerates exactly what each story carries (title, link, points, comment count, author, age, discussion URL). No sibling in the list covers HN content, so there is nothing to confuse it with.

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 to follow what developers are discussing right now" gives a clear situational cue, and "Example: count=5" shows a typical call. It stops short of stating when-not to use it or naming an alternative source for non-HN content, so it is context-rich but not exclusionary.

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