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

Annotations already declare readOnly, idempotent, openWorld and non-destructive, so the safety profile is covered. The description goes further by disclosing the payload composition (default values plus a derived cost at the current certificate price plus regulation links) and that access is free — genuinely useful context beyond the structured fields. It stops short of noting what happens when no default exists for a code/country.

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 sentence that front-loads the resource and then appends output details, plus a one-word 'Free.' fragment. It is slightly run-on, but nothing is padded and the most important clause comes first.

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 must carry the return-value burden, and it does partially by naming values, cost per tonne and regulation links. It omits response format, units/precision, behaviour when defaults are unavailable, and any pagination, which leaves real gaps for a data-retrieval 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 description coverage is 100%, including the non-obvious 'omit country for the other countries value' rule, so the schema does the heavy lifting. The description only restates the keys ('for a CN code, by country of origin and year') without adding format or fallback semantics. 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?

The description names a precise resource — CBAM default embedded-emission values for a CN code, keyed by country of origin and year — and adds what else the response carries (cost per tonne, regulation links). That distinguishes it implicitly from cbam_certificate_price (the price itself) and cbam_countries, though no sibling is named explicitly. Clear, but without the explicit differentiation a 5 requires.

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?

There is no statement of when to reach for this tool instead of cbam_certificate_price or cbam_countries, and no prerequisites or exclusions. 'Free' signals cost/entitlement, not usage context, so an agent gets no routing help.

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