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

Annotations already declare the safety profile (readOnly, idempotent, non-destructive, closed-world), so the bar is lower; the description adds behavior the annotations do not, notably that `count` is null when below the public minimum. It also discloses that results carry two distinct URLs and what each means, which is genuine operational context.

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?

Three sentences, none wasted: scope first, then the trigger condition, then the return-shape clarification. Front-loaded and dense with no filler or restatement of the title.

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 usefully compensates by naming the key return fields and the null-count edge case. The one unresolved point is whether the three leaderboard windows are all returned together or separately, which an agent might need; everything else is covered.

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?

The tool takes zero parameters, so the baseline is 4. The description documents result fields (listingUrl, url, count) rather than inputs, which is the only thing parameter semantics could add here.

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 resource (trending leaderboards on this directory) and enumerates the three scopes it covers: most viewed today, most clicked this week, most voted this month. An agent can immediately distinguish this from search_listings or browse_category, which do not surface popularity rankings.

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 it when a user asks what is popular, new or trending" gives an explicit trigger condition, which is better than most catalog tools. It stops short of naming the alternatives (e.g. search_listings with a sort parameter) or stating when-not to use it, so it is clear context without exclusions.

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