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

Annotations already declare readOnlyHint=true and openWorldHint=true, so the safety and openness profile is covered. The description adds the 'one index family' and 'current or historical' scope constraints, but says nothing about pagination, ranking size, or update cadence. With annotations doing the heavy lifting, this is adequate rather than rich.

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 waste. The core purpose is front-loaded and the routing hint follows immediately, with no redundant restatement of the name or schema.

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, so return values need not be explained, and the description covers purpose and the primary alternative. For a three-parameter read tool this is nearly complete, lacking only minor scope notes like ranking size or update frequency.

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 the schema already documents index, scope, and period (including the period requirement when scope=historical). The description adds no syntax or format detail beyond that, matching the baseline for high schema coverage.

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 ('Fetch') and resource ('global Numbeo city ranking'), scoped to 'one current or historical index family'. It also names the sibling it is not (numbeo_indices_rankings_by_country), so an agent can distinguish it without opening either 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?

Explicitly routes the agent to numbeo_indices_rankings_by_country for the country-grouped view, giving a clear when-to-use-this-vs-that rule. It doesn't mention the other nearby siblings (numbeo_indices_city, numbeo_indices_country), so it stops just short of full alternative coverage.

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