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

Annotations already declare read-only, idempotent, non-destructive, and closed-world behavior, so the safety profile is covered. The description adds two things annotations cannot express: the credit cost (15 credits/15p) and the geographic coverage limit, both of which materially affect whether an agent should call it.

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 resource and key, then use case, then constraints and cost. No filler, and each sentence carries distinct information.

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?

An output schema exists, so return values need no explanation, and cost plus geography are covered. The only gap is pagination/limit behavior for portfolios larger than the default 500 titles, which matters given this tool's stated portfolio-mapping purpose.

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 0%, so the description carries the full burden. It clarifies that company_number is a Companies House number, but says nothing about the limit parameter (default 500) or what happens when a portfolio exceeds it — a real risk for large landlords.

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 resource (titles held) and the exact key it is indexed by (Companies House number), with a concrete use case (portfolio mapping). It implicitly distinguishes itself from the sibling ownership_by_title, but never names that sibling to make the reverse-lookup distinction explicit.

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?

'Useful for mapping a landlord's or developer's portfolio' gives clear usage context, and 'England & Wales only' functions as an explicit when-not constraint for Scottish/NI data. It stops short of naming the alternative tool (ownership_by_title) for the opposite query direction.

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