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

Annotations already declare readOnly, idempotent, non-destructive and closed-world, so the safety profile is covered. The description adds genuinely useful non-annotation context: the 15-credit cost and the England & Wales coverage limit. Return format/pagination is not described, keeping it from a 5.

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?

Three short sentences, front-loaded with the purpose followed by the use case and then the constraints. No filler, though the cost/geography lines could be tightened into one.

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 an output schema present, return values need not be explained, and the description covers purpose, coverage area, and cost. The gap is the undocumented limit/pagination semantics, which matters for a collection-returning tool.

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 0% across two parameters, so the description carries the burden. It identifies company_number in prose ('by Companies House number') but gives no format or validation detail, and the limit parameter is not mentioned at all, leaving result-size control undocumented.

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?

States a specific verb+resource (titles held by a company) and the keying identifier (Companies House number), and adds a use case (mapping a landlord's or developer's portfolio). It does not explicitly distinguish itself from the sibling ownership_by_title, so it stops short of a 5.

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 implied usage via the portfolio-mapping use case and states the England & Wales geographic constraint, which is a real selection signal. But it never says when to prefer this over ownership_by_title or owner_profile, so the routing guidance is only implied.

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