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

Annotations already declare readOnly, idempotent, non-destructive, closed-world behavior, so the safety profile is covered. The description adds genuinely useful context beyond that: it explains the shape of the returned data (total plus per-vertical and per-event_type counts) and its purpose for filter discovery, which matters because there is no output schema.

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?

Two sentences, zero filler, with the data-shape statement front-loaded and the usage guidance immediately after. Every clause earns its place.

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 zero-parameter tool with no output schema, the description covers what is returned and why to call it, which is essentially everything an agent needs to invoke it correctly. Minor gap: it does not characterize the response format (e.g., map vs. list), though that is hard to state without an output schema.

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 of 4 applies. The description correctly implies an unfiltered global aggregate and does not need to explain parameter syntax that does not exist.

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 states precisely what the tool returns: a total item count plus breakdowns per vertical and per event_type. It is a clear verb-less but unambiguous read-only stats resource, distinguishable from get_latest_news/search_news by being a coverage/enumeration tool. It stops short of explicitly naming the siblings it is not.

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 discover valid filter values and where coverage is dense" gives a concrete when-to-use case tied to the sibling search tools, telling the agent to call this before filtering. There is no explicit when-not or named alternative, so it falls short of a 5.

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