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

With no annotations at all, the description carries the full burden and does a decent job: it discloses the paid model ($0.002 USDC on Base), that no account or API key is needed, the backing endpoint URL, and the shape of the payload (points, comments, links). It does not cover payment failure behavior, rate limits, or latency/response envelope, which keeps it below 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 compact paragraph that front-loads the most decision-relevant token ('Paid'), then topic, ordering, payload, price, auth requirements, and endpoint. No sentence is padding and nothing is buried.

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?

For a two-optional-parameter read/paid tool with no output schema, the description supplies the cost, auth posture, return fields, and ordering default — enough to invoke it correctly. The remaining omission is what a caller gets on payment or upstream failure, which is a minor gap given the low complexity.

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 two parameters are already documented. The description only reinforces defaults ('newest first (or sort=top)') without adding format or edge-case meaning (for example what n values are accepted or what happens if n exceeds the 1-30 range). That matches the baseline 3 for a fully covered schema.

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 the resource precisely: Hacker News stories filtered to the 'python' topic, with the default ordering (newest first) and the fields returned (points, comments, links). It never names a sibling, so the agent must infer that buy_hn is the unfiltered general feed and buy_hn_rust/javascript/etc. are topic peers, but the topic suffix makes the distinction fairly obvious.

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 topic label: this is the tool for python-related HN content. There is no explicit when-to-use statement, no exclusion, and no pointer to buy_hn (general) or buy_hn_ai-agents/llm as alternatives when the query is broader or narrower than 'python'.

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