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

Annotations already establish the safe-read profile (readOnlyHint, idempotentHint, destructiveHint=false), so the description's real contribution is the billing/rate-limit disclosure (daily free allowance, then $0.001 USDC per call via x402), which is genuinely useful behavioral context an agent cannot get from annotations. It stops short of describing response shape, though the output schema covers that.

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?

Two tight sentences with zero filler: the returned hierarchy is front-loaded and the cost caveat follows. Every clause carries 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?

Safety profile comes from annotations and return values from the output schema, so the description only needs to add scope and cost, which it does. The one gap is that the required ONS LAD code has no pointer to how an agent should obtain or validate it, despite a relevant uk-geography__search sibling.

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 there is a single required string parameter documented as an 'ONS local authority district code', so the schema does the heavy lifting. The description adds domain color about what that code resolves to but no format, validation, or example details beyond the schema; baseline 3 applies.

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 and the payload it returns (county/unitary, region, country, wards, constituencies) for a given local authority district, which distinguishes it from uk-geography__county or uk-geography__region by making clear it resolves a district code into its containing hierarchy. It does not explicitly name those siblings, so an agent must infer the distinction.

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?

No when-to-use or when-not-to-use guidance is given, and no alternative is named. The only conditional statement concerns billing ('free within the daily allowance, then $0.001 USDC per call'), which is pricing rather than invocation guidance; nothing tells the agent to first obtain a code via uk-geography__search.

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