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

Annotations already declare readOnlyHint, idempotentHint, openWorldHint and destructiveHint=false, so the safety profile is covered. The description adds non-obvious behavior beyond that: the precedence of elfCode over localName and the fact that regionCode is only relevant for region-varying countries. It does not disclose failure behavior when no match is found.

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 front-loaded sentence with the verb, the resource, and the lookup precedence packed in; no filler, no restatement of the title, and the optional-region caveat is placed last where it belongs.

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 four-parameter read-only lookup with full schema coverage and annotations covering safety, the description is nearly sufficient — it explains purpose, precedence, and region scoping. The one gap is that with no output schema it does not indicate what is returned or what happens on a miss, which for a lookup tool an agent would benefit from knowing.

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%, so all four parameters are already documented with examples (H8VP, Anpartsselskab, DK). The description adds meaning the schema does not: the lookup precedence between elfCode and localName, and the conditional applicability of regionCode. That is a modest but real gain over the baseline 3.

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 (looks up) and a precisely scoped resource (an entity legal form from the ISO 20275 ELF code list, within a country). The ISO standard reference and the country scoping make the tool unmistakable, and no sibling (create_user, get_lei_record, get_prices, search_lei_by_company_name) overlaps with it.

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 gives an explicit resolution order — 'by ELF code first, otherwise by the legal form's local name, optionally within a region' — which tells the agent exactly which parameter to prefer and when regionCode applies. It stops short of stating what to do when neither code nor name resolves, so it is clear context rather than a full when/when-not guide.

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