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

Annotations cover safety (readOnly, openWorld), but the description adds real value beyond them: a hard 8-item page cap with cursor pagination, silent skipping of deleted/dead replies, plain-text normalization of item bodies, and the exact field set returned. It also discloses the billing model ($0.01 per successful call, not charged for misses) and the x402 payment mechanism, which no structured field carries.

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?

Front-loads the identity of the resource, then pagination, then returned fields, then pricing — a sensible order with little waste. The final pricing/payment sentence is dense and slightly run-on, but every clause carries information an agent needs.

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 compensates by enumerating the per-item fields (text, author, score, reply count, parent, time) and the shared social schema. Combined with pagination and charge semantics, nothing material is missing for correct invocation.

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%, so the baseline is 3, but the description adds meaning the schema does not: a call returns at most 8 items regardless of the requested limit, with next_cursor paging the remainder. That clarifies the limit/cursor interaction and explains why reply counts may appear truncated.

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 a specific verb and resource: fetch one Hacker News story or comment by id or news.ycombinator.com URL, together with its direct replies. The 'one item by id/URL' framing contrasts implicitly but clearly with the hackernews_search sibling, so an agent can pick without opening either schema.

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?

Gives clear operational context: up to 8 replies per call, next_cursor to page, deleted and dead replies skipped. It stops short of explicitly naming hackernews_search as the alternative for lookups without an id, so routing is implied rather than stated.

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