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

Annotations already declare readOnly/idempotent and closed-world, so the bar is lower; the description still adds real context the annotations do not carry: the $0.05-per-call x402 (USDC on Base) payment model, the default value of 'include', and what the response contains. It omits error behavior and rate limits, so a 4 rather than 5.

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 dense paragraph but front-loaded with purpose and modes, then coverage, then return content, then price. Every clause carries information, though the first sentence packs several modes into one long clause chain.

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 does the work of describing returns (Latin and local-language names plus urbanisation, coastal and mountain typologies), scope, and pricing. It leaves the shape of hierarchy responses (how parents/children are returned) unspecified, so not quite a 5.

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 every parameter is already documented in the schema. The description reinforces the code/hierarchy/name-search modes but adds no syntax or format detail beyond what the schema properties provide, making the baseline 3 correct.

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 ('NUTS region lookup') and enumerates the three operating modes: resolve a code to name/country/level, walk the hierarchy, or search by name. Explicitly scoped as EU statistical regions with NUTS 2024 coverage, which separates it from the generic country_lookup sibling.

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 description makes clear which task each mode serves (code resolution vs. hierarchy traversal vs. name search), so an agent can pick the right call. It stops short of naming a sibling as an alternative or stating explicit exclusions, which keeps it from a 5.

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