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

Going beyond the readOnlyHint/idempotentHint annotations, it discloses the response shape (supplied inputs, missing information, null metric values), explicitly states no proposed habitat or condition is assumed, and warns that a competent ecologist and the current official metric are still required. The chaining note on site_ref reuse is genuinely useful behavioural context for a read-only, open-world tool.

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?

Labelled sections (Purpose / When to use / Returns / Limitations / Parameter guidance / Chaining) front-load the essentials and are easy to scan. It is slightly longer than needed, with minor overlap between 'no proposed habitat or condition is assumed' and the schema's 'no default is assumed'.

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?

With an output schema, full annotation coverage and 100% parameter coverage already present, the description supplies exactly the extra layers an agent needs: scope boundaries, non-calculations, and the site_ref chaining contract. Nothing material for correct invocation is missing.

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 100%, so 3 is the baseline, but the description adds real meaning: it flags current_habitat_type as the one to supply, marks site_area_ha and proposed_habitat_type as optional, and states no defaults are assumed. It does not clarify the site_ref passthrough contract beyond what the schema's own description already says.

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 concrete verb and artifact: prepare an England biodiversity evidence checklist from a site area and habitat labels. The biodiversity/BNG scope is specific enough to separate it from the sibling prepare_heritage_review, prepare_sequential_review and prepare_building_regulations_review tools without opening any schema.

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 'When to use' line gives a clear trigger (identify missing surveys and metric inputs before a BNG review) and the Limitations line enumerates what it will not do: units, uplift, exemptions, offsets, irreplaceable habitat. It stops short of naming a specific alternative sibling for those excluded jobs, so the agent must infer the fallback.

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