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

Annotations already declare readOnly, idempotent and openWorld. The description adds genuinely new behavioral context: a per-call cost of 0.005 USDC on Base with free errors, which an agent needs before invoking a paid tool. It stops short of describing rate limits or response shape.

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, front-loaded with the data scope and followed by the pricing note. No redundancy and nothing that could be trimmed without losing information.

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 output schema, the description carries the burden of explaining returns and does so by naming the four metrics covered. It lacks detail on response structure/units, but is otherwise sufficient for correct invocation of a two-optional-parameter tool.

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%, so the baseline is 3. The description adds value beyond the schema by constraining the year parameter to 1951–latest (the schema only enforces a 4-digit pattern) and by naming what data is returned per region/year (population on 1 January plus births, deaths, migration).

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+resource ('Statistics Norway's population') with explicit geographic granularity (country, county, municipality) and temporal range (1951 to latest year). No sibling tool covers population data, and the title/description make the scope unambiguous.

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?

Implicitly guides usage through scope constraints: one region at a time, years from 1951 to latest, defaulting to the latest year. It does not explicitly state when-not-to-use or point to an alternative, but no sibling tool overlaps, so there is little to disambiguate.

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