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

Annotations already declare readOnly/idempotent/openWorld/non-destructive, and the description adds what structured fields cannot: the cost per call (0.008 USDC or 4 credits), the free-first-5-per-day policy, and the auth mechanic that an api_key can be passed inline without reconnecting. It also enumerates the returned fields, so the agent knows the payload shape despite there being no output 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?

Front-loaded with the routing decision, then the register coverage, then returns, then cost. The long register enumeration is dense but earns its place by defining scope; only slight trimming would be 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 compensates by listing the returned fields explicitly. Payment model, auth requirement, coverage and lookup modes are all present, leaving nothing an agent needs in order to call it correctly.

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 parameters are documented structurally. The description adds value beyond that by stating the two lookup modes (name or id) and by listing which countries have registers, which is what actually makes the optional country filter meaningful.

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?

Specific verb+resource: confirms a company exists and is active against named official registers. It explicitly positions itself as the cheap first step before a dossier, which cleanly separates it from company_dossier, company_health, eu_company_check and us_company_lookup.

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?

States the exact selection condition ("only need to confirm a company exists and is active") and routes the agent to the more expensive dossier when that is insufficient. It also spells out the payment paths and the free-tier allowance, so the agent knows when no credentials are needed.

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