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

Annotations already declare readOnlyHint=true and openWorldHint=true, so the safety profile is covered. The description adds that rankings can be pulled for current or historical snapshots, which is useful context, but it says nothing about return format, ordering, or coverage limits beyond what annotations and the output schema carry.

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 front-loaded sentence that names the resource and scope with no filler. It is efficient, though it is on the terse side for a tool with a conditional historical-period argument.

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?

An output schema exists and all three parameters are fully described in the schema, so the description need not explain returns or parameter formats. What remains thin is sibling routing, but the structural fields carry most of the load.

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 description coverage is 100%, so index, scope, and period are all documented in the schema itself. The description echoes the scope axis ('current or historical') but adds no syntax or format detail beyond that, so the baseline 3 applies.

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: a global city ranking over an index family. The word 'city' implicitly distinguishes it from numbeo_indices_rankings_by_country and the country/city detail siblings, so an agent can route reasonably well without opening the 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?

The parenthetical '(current or historical)' hints at the historical-snapshot use case, but no alternative tool is named and there is no explicit when-to-use vs. numbeo_indices_rankings_by_country guidance. Usage is only implied.

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