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

Annotations already cover the safety profile (readOnlyHint=true, openWorldHint=true), so the bar is lower. The description still adds value by disclosing that the data is credential-free public Numbeo data (no auth required) and that results cover both a country aggregate and every tracked city's breakdown. It does not mention rate limits or freshness, but the auth context is a genuine addition beyond annotations.

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 tight sentences with zero waste; the scope and payload are front-loaded before the sibling routing. 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 two-parameter read-only tool with full schema coverage, annotations declaring read safety, and a dedicated output schema, the description supplies everything an agent needs: scope, payload shape, data provenance, and the alternative tool. Nothing material 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?

Schema coverage is 100% and both parameters carry their own descriptions (index enumerates the seven families, country gives the Numbeo spelling). The description's 'index family' and 'one country's' phrasing adds only marginal framing beyond the schema, so the baseline 3 is appropriate.

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 (Returns) and resource (one country's aggregate data for a Numbeo index family) and clarifies the payload includes every tracked city with its index breakdown. It also names the sibling numbeo_indices_city, so an agent can distinguish the country-scoped tool from the city-scoped one without reading 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?

The final sentence explicitly routes the agent: 'Use numbeo_indices_city to get a Numbeo city's data for an index family,' naming the alternative and the condition that selects it. This is a clear when-to-use-the-other-tool instruction rather than implied context.

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