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

Annotations already declare readOnlyHint, idempotentHint and openWorldHint, so the description is free to add scope detail — and it does: it defines exactly which registers are covered, specifies that US coverage requires an LEI, and states the exclusions ('Companies only, no directors or contact details'). Not disclosing pagination/no-match behavior keeps it from a 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?

Two sentences, front-loaded with the action and the returned fields, then the coverage list. The country enumeration is long but each element is decision-relevant; only minor trimming (e.g. the parenthetical about state filing numbers) is possible.

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 return-value burden and does so by naming the fields returned and their consistent shape. The remaining gap is operational: no statement about what happens on zero results or how limit interacts with ranking, which for a 4-parameter search tool is a real but modest omission.

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 genuine meaning: it constrains the country parameter to the supported register set and explains the LEI condition that governs whether the state parameter applies to a US entity. That is useful context beyond the schema's own text.

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 ('Searches one country's official company register by name') and enumerates both the coverage (GB, NO, FR, FI, CZ, SK, IE, AU, LEI, US) and the returned shape. It is clear this is official-register data, but it never names siblings like company_search or company_lookup to draw the boundary explicitly.

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?

Usage is implied by the coverage list and the 'official register' framing, so an agent can infer this is the authoritative-source option. However, there is no explicit when-to-use / when-not statement and no mention of company_search or company_lookup as alternatives, which matters given three similarly named siblings.

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