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

Annotations already declare readOnly/idempotent/non-destructive/closed-world, and the description adds substantial behavioral context beyond them: the unknown-coverage exclusion rule when a ceiling is set, the fact that only ~41% of parcels have measured coverage, UK-only geographic restriction, and a 30-credit cost. These are high-value caveats an agent cannot get from structured fields.

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?

Purpose is front-loaded, followed by the key data-caveat and cost lines. Every sentence adds information and there is no filler. The mid-sentence line breaks are slightly awkward but do not impede reading.

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-format explanation is unnecessary. The description covers the important semantic trap (unknown coverage vs. zero coverage), geography, and cost. It is nearly complete, only lacking coverage of the non-required parameters.

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%, so the description carries the burden. It explains max_built_coverage well (a 'ceiling' with exclusion semantics), but says nothing about area_id, limit, or min_area_m2, leaving three of four parameters defined only by their bare titles and defaults.

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?

The opening line states a specific resource and scope: 'Land parcels by size and how much of them is built on.' An agent can infer this returns parcels with built-coverage attributes. It does not explicitly differentiate itself from nearby siblings like parcel_lookup or land_assembly, so it falls 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?

'Set max_built_coverage to 0.2 to find largely undeveloped plots' gives a concrete usage scenario for one parameter, and the exclusion rule clarifies when results change. However, there is no explicit comparison to alternative tools, no when-not-to-use guidance, and no guidance on the other parameters.

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