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

Annotations already declare readOnlyHint, idempotentHint, destructiveHint=false and openWorldHint=false, so safety is covered. The description adds two things annotations cannot: a per-call cost of 15 credits (15p) and a geographic eligibility restriction — both material to an agent deciding whether to call.

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 lines, zero padding, with the core capability front-loaded ahead of the scope and cost constraints. It is arguably over-terse — the fragments 'England & Wales only' and 'Costs 15 credits' could be framed as explicit constraints — but nothing is wasted.

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 here, and the annotations carry the safety profile. For a one-parameter, metered lookup the description is nearly sufficient; the remaining gap is how to supply or validate a title number and what is returned on a miss (including whether credits are still charged).

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% for the single required parameter, so the sole parameter is undocumented in structured form. The description partially compensates by naming it an 'HMLR title number', which tells the agent the expected identifier source, but gives no format example, validation rule, or behaviour when the title does not exist.

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 (registered proprietors) and the exact lookup key (an HMLR title number), and adds jurisdictional scope (England & Wales only). It implicitly distinguishes itself from ownership_by_company by keying on title rather than company, though it never names that sibling explicitly.

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?

Usage is implied rather than stated: an agent can infer this is the tool for 'who owns title X', and the England & Wales restriction usefully excludes Scottish/NI titles. But there is no explicit guidance on when to prefer ownership_by_company, owner_profile, property_lookup, or parcel_lookup instead, or how to obtain a title number first.

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