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

Annotations already declare readOnlyHint, openWorldHint and idempotentHint, so the safety profile is covered. The description adds genuinely new behavioral context: a per-call cost of 0.005 USDC via x402 on Base, that errors are free, and that the data is 'cleaned' registry data — none of which appears in the annotations or schema.

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 tight sentences, front-loaded with the resource and registry source, then the returned fields, then the cost model. The field enumeration is dense but earns its place since there is no output schema.

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 compensates by listing the returned field set (status values, company form, industry, address, website, names, EU ID). It also discloses cost and error pricing, leaving nothing an agent needs before calling.

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 a described businessId including the Y-tunnus format, an example and a mod-11 check note. The description adds no parameter-level detail beyond the schema, so the 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?

States a specific verb+resource ('One Finnish company from the PRH trade register (YTJ)') and enumerates the fields returned, which makes the payload shape predictable. It does not explicitly contrast itself with the sibling get_company or search_finnish_companies, so an agent must infer the distinction from 'Finnish' and the singular 'One'.

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 only implied: 'One Finnish company' hints this is a single-record lookup rather than a search, which helps against search_finnish_companies. There is no explicit when-to-use or when-not-to-use statement, and no routing to alternatives for name-based discovery.

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