Look up a company (ЕИК / VAT)

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

With readOnlyHint=true already declared, the description doesn't need to restate safety. It adds useful context: the lookup happens via external sources ('Commercial Register / VIES') and warns 'Never invent an EIK', which is a behavioral constraint. However, it omits details like potential multiple results for name searches or error behavior, which would be relevant for an agent. The description is adequate but not rich.

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?

The description is two sentences, each earning its place: the first states the core capability, the second adds critical usage guidance. It is front-loaded with the verb and resource, and no filler or redundancy exists. The warning 'Never invent an EIK' is a valuable addition in the same sentence.

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?

The tool has no output schema, so the description should clarify what is returned. It states 'get the exact legal name and VAT number', but doesn't specify the response structure or whether name searches may return multiple matches. The tool is simple with all optional parameters, but the lack of return-type information leaves the agent guessing about the result shape. While not severely incomplete, it's a noticeable gap.

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?

The schema already provides full descriptions for all three parameters (coverage 100%), including patterns and examples. The description only says you can look up by EIK, VAT, or name, which mirrors the schema without adding new semantics. Since the schema already carries the burden, a baseline score of 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?

The description states a specific verb ('Look up') and the resource ('a company by Bulgarian EIK, EU VAT number or name via nula.bg'). The purpose is unambiguous and clearly distinct from sibling tools like invoice/bill management or customer search. The added usage context (before creating an invoice) further disambiguates its role.

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 explicitly states when to use this tool: 'Use it BEFORE creating an invoice or bill for a counterparty you have not seen'. This provides clear contextual guidance. However, it does not mention alternatives (e.g., nula_search_customers) or explicitly state when not to use it, so it stops short of a full when/when-not contrast.

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