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

With readOnlyHint=true already covering safety, the description adds useful domain behavior: three procurement routes, spatial risk multipliers 1.0/0.75/0.5, two Defra credits per unit, and England-only scope. It does not explain return values, but an output schema exists, and nothing contradicts the annotations.

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?

The description is one dense, run-on sentence with nested parentheticals. It is front-loaded with the core purpose and has little obvious filler, but the structure makes details such as 'priced per unit at two Defra credits per unit' hard to parse.

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?

For a read-only estimator with an output schema and four parameters, the description supplies key domain context: England-only scope, mandatory 10% BNG, procurement routes, risk multipliers, and land types. The main missing pieces are explicit lat/lon semantics and sibling routing, so it is complete enough but not exhaustive.

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 must carry parameter meaning. It explains scheme_ha as hectares and land_type values, and hints that lat/lon identify 'this point's authority names,' but it never clearly defines the required lat/lon inputs or formats.

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 description gives a specific verb and resource: estimating the cost of meeting England's mandatory 10% BNG requirement, with scope details such as scheme hectares and three procurement routes. It is clear but does not explicitly distinguish this tool from the sibling estimate_bng_income.

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?

It identifies the applicable scenario (England development schemes subject to mandatory 10% BNG) and an exclusion ('England only'), plus the practical note 'Free, no key.' It does not name estimate_bng_income or explain when to choose this cost estimator over that income estimator.

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