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

Annotations already declare readOnly, idempotent, openWorld and non-destructive, so safety is covered. The description earns credit for disclosing the cost model (0.008 USDC via x402 or 4 credits), the x402 payment path, and the free-tier allowance of five paid calls per day — none of which the annotations convey. It doesn't say what a no-match result looks like, which is the main remaining behavioral gap.

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 use condition, then scope, then outputs, then pricing — the right order for an agent scanning for a decision. The registry enumeration is long but each entry conveys real coverage information, so it mostly earns its place.

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 read-only lookup with no output schema, the description supplies the return fields, the registry coverage, the lookup keys and the payment semantics. The one meaningful omission is disambiguating this tool from its many siblings and stating the minimum viable input, given that all params are optional.

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% with all three parameters documented, so the baseline is 3. The description adds the useful hint that id accepts LEI/SIREN/UK/Irish/Estonian identifiers and ties the registry list to country selection, but it never clarifies the combination rule — notably that zero parameters are required, so an agent could legally call with no arguments.

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?

A specific verb+resource (verify a company exists and is active) with the registries covered, the return fields, and the two lookup keys (name or id) all named. It stops short of distinguishing itself from overlapping siblings such as us_company_lookup, eu_company_check, company_dossier or company_health, so an agent can't tell from the text which one to pick.

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?

"Use when you need to verify that a company exists and is active" is a real trigger condition, which is more than implied usage. But with seven-plus near-neighbour tools in the sibling list, there are no exclusions, no routing rule (e.g. use us_company_lookup for US-only), and no statement of what to do when the register isn't in the covered list.

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