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

Annotations already declare readOnlyHint=true, idempotentHint=true, destructiveHint=false, and openWorldHint=false, so the safety profile is fully covered by structured data. The description adds only that the content is a coverage catalog (metros, cities, categories) and says nothing about size, pagination, or freshness of the list. With annotations carrying the burden, a 3 is appropriate.

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 short sentences with zero filler: the first states what is returned, the second states when to call it. Front-loaded and appropriately sized for a no-argument lookup tool.

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 parameters, no output schema, and full annotation coverage, the description only needs to say what data comes back and when to call it — both of which it does. It could be slightly stronger by noting the granularity (e.g., whether results are grouped by metro or flat), but nothing essential is missing.

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; there is no parameter syntax for the description to clarify. No misleading parameter hints are present.

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 exact resource returned (metros, cities, and categories), so an agent knows this is a static coverage catalog rather than an event lookup. It lacks an explicit verb like 'list' and does not contrast itself with get_event or search_events, but the resource is specific enough to be distinguishable.

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?

'Call it when unsure whether a city is covered' gives a concrete triggering condition, which is exactly the right guidance for a reference-lookup tool. It does not name alternatives or exclusions, but the sibling tools (get_event, search_events) are clearly different operations, so no routing ambiguity remains.

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