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

Annotations already declare readOnly/idempotent/openWorld/non-destructive, so safety is covered. The description adds genuinely new behavioral context beyond them: sole proprietors are excluded from results, coverage is limited to FR and NO registers, and the status values returned (active, ceased, bankrupt, being wound up) tell the agent what a result can mean. The return-field list is somewhat redundant given an output schema exists.

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 trigger condition and examples, then exclusions — a sensible order with no filler sentences. It is somewhat long, and the enumeration of every returned field duplicates the output schema, but nothing is padded for its own sake.

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 two-country registry lookup with an output schema, the description covers the trigger, the exclusions, the country/identifier formats, and the coverage limitation (sole proprietors omitted). An agent has everything needed to decide whether to call it and how.

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 description coverage is 100%, so the baseline is 3. The description restates that query takes a name or registration number with SIREN/organisation-number formats, which the schema already documents field-by-field, and says nothing about the limit parameter beyond what the schema specifies.

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+resource ('look up a French or Norwegian company') and immediately scopes it to two national registers, which cleanly separates it from siblings like find_company_lei and check_vat_number. Concrete example queries ('who is behind SIREN 552032534?') make the target intent unmistakable.

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 states when to use the tool (company registered in France or Norway), gives three illustrative queries, and then explicitly enumerates when NOT to use it: other countries, owners, directors, private persons, accounts and credit ratings. That is a near-complete routing rule set even though sibling names are not cited.

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