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

Annotations already mark readOnlyHint and idempotentHint, so the safety profile is covered. The description adds valuable behavioral context beyond annotations: pagination cap (up to 50/page), the possibility of hundreds of sub-units for large companies (response scale), and data provenance (Brønnøysundregistrene, NLOD 2.0). No contradiction with 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 earning its place: purpose, field composition, use case, scale/pagination/source. The core function is front-loaded and no redundant words appear. The length is justified by the information density.

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 read-only list tool with a 100%-covered schema, present output schema, and annotations covering safety, the description covers everything a caller needs: what the tool returns, pagination, scale expectations, and data source. Nothing essential is missing.

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% and the schema already documents org_number, page, and size with format/range details. The description adds general context about sub-unit composition, but not parameter-specific semantics beyond what the schema provides. 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?

The description opens with a specific verb (List), a clear resource (registered sub-units/underenheter), and an explicit scope (for a Norwegian parent company). It enumerates concrete examples (branches, departments, production sites, physical locations) and names what each sub-unit contains, making it easy to distinguish from sibling tools like brreg.registry.entity or brreg.registry.search.

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 states a clear use case ('useful for mapping a company's operational footprint across Norway') and the pagination behavior. However, it does not explicitly mention when not to use this tool or point to alternatives like brreg.registry.search for finding the parent company first, so it stops short of full exclusion guidance.

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