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

Annotations already declare readOnly, idempotent and closed-world, so the safety profile is covered. The description goes beyond structured data by disclosing the cost model ($0.05 per successful call over x402/USDC on Base), the exact classification edition (NUTS 2024), and the returned fields including typologies — genuinely useful behavioral context.

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?

Front-loaded with the core action, then capability scope, then returns, then pricing — a sensible order. Three dense sentences with little waste, though the mid-sentence enumeration of capabilities is somewhat packed.

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 correctly summarizes what comes back (Latin-script and local names, country, level, typologies) and adds cost and coverage details. Only minor gaps remain, e.g. behavior on no-match or how many regions exist per level.

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, but the description adds real meaning: it maps level numbers to their human labels (country, major region, basic region, small region) and names the hierarchy directions (parents/children) that the 'include' parameter controls, which the schema only lists as bare tokens.

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 ('Look up a NUTS statistical region of the European Union') and enumerates the three operating modes: resolve a code, walk up/down the hierarchy, or search by name. This clearly distinguishes it from siblings like ref_country, ref_airport and ref_currency.

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 the mode selection clear (code lookup vs. hierarchy walk vs. name search) and states the coverage scope, giving the agent enough context to pick it over siblings. It does not, however, state any when-not conditions or name alternative tools for overlapping needs.

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