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

Annotations already declare readOnlyHint=true, idempotentHint=true, destructiveHint=false and openWorldHint=false, so the safety profile is fully covered by structured data. The description adds two things beyond that: the aggregation behaviour ('in one call') and the cost signal ('Free'). It does not discuss precedence when both inputs are supplied, failure behaviour for an invalid postcode, or coverage latency, so the added behavioural value is modest.

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?

Front-loaded with the outcome ('every planning designation ... in one call') before the enumeration, and the input rules are compressed into two short lines. The 13-item designation list is long but each item is query-relevant vocabulary rather than filler, so it earns its place. Slight redundancy between the title and the opening clause.

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-value detail is correctly omitted, and the description covers scope, dual input formats, geography, and cost. What is missing for a fully self-contained definition is input arbitration (both supplied, neither supplied) and any note on invalid postcode handling. For a two-parameter read-only lookup, the remainder is close to sufficient.

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% — the two properties have no descriptions at all — so the description carries the full burden, and it does specify the expected format for each: 'full UK postcode' and 'location as "lat,lng"'. That format detail is genuinely load-bearing since nothing in the schema conveys it. The gap is that it doesn't say whether at least one is required (schema marks neither required), what happens if both are given, or which wins.

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 and scope: every planning designation affecting a location, returned in one call. The enumeration of 13 designation types (conservation area, listed building, green belt, AONB, flood zone, TPO, etc.) makes the tool's content unmistakable and separates it by implication from planning_applications or property_planning_history. It stops short of explicitly naming the sibling it is not, which keeps it out of 5 territory.

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 gives useful boundaries — 'UK only' and 'Free' — and tells the agent how to supply input, but it never says when to prefer this over neighbours like planning_check, planning_applications, or property_flood_risk. Usage is implied by the purpose statement rather than stated as a when/when-not rule.

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