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

Annotations only cover readOnly/openWorld, so the description carries the real behavioral load and does: it lists the returned field set, warns that field coverage varies by country, and explains that missing fields are annotated as not_published_by_registry, not_collected, or unknown. That is material disclosure an agent cannot get from the annotations.

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?

Four sentences, each doing work: identity/scope first, then usage, then return shape, then the negative constraint. Only slight redundancy in restating the search alternative twice.

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?

No output schema exists, but the description compensates by enumerating returned fields and the null-explanation semantics. Coverage caveats and the exact-identifier precondition round out everything needed to call this correctly against five siblings.

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 75%, so the schema documents most parameters. The description still adds meaning by grounding registry_id with concrete national examples (FR SIREN, GB CRN, SE organisationsnummer) and stressing exactness, which goes beyond the schema's terse 'National registry identifier' text. It says nothing about the include/include_nulls expansions, a minor gap.

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 opens with a specific verb and resource plus the exact lookup key: 'Retrieve one FirmaDB company record by exact (country, registry_id).' It enumerates the returned fields and clearly separates this exact-identifier lookup from the fuzzy-name sibling.

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?

It gives explicit when-to-use ('after firmadb_search_companies has identified the target, or when the user already has an official national registry identifier') and an explicit when-not-to-use directive ('Do NOT use this for fuzzy name lookup — call firmadb_search_companies first'). The alternative is named, not implied.

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