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

Annotations already declare readOnly, idempotent, openWorld and non-destructive, so the safety profile is covered. The description adds genuinely new behavior: the free daily allowance and the $0.002 USDC x402 fallback charge, which is real operational context an agent should factor in.

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?

Three short front-loaded fragments: what it returns, how to locate, and cost. Zero wasted words and the most important fact (the resource) leads.

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 a full input schema, an output schema, and rich annotations, the description carries the residual burden of locator modes and pricing, which it covers. It is complete enough to call correctly; only the link to sibling designation datasets is absent.

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%, so all five parameters (lat, lng, geometry, postcode, include_ended) are already documented. The description only restates the postcode-vs-lat/lng choice and adds nothing about the geometry or include_ended options, so it stays at the baseline.

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 (SSSIs) and the spatial scope (covering a point), so the agent knows exactly what is returned. It does not explicitly differentiate from designation siblings such as ramsar, special-area-of-conservation, or local-nature-reserve, leaving that to the tool name.

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?

Gives the two accepted locator modes (UK postcode or lat/lng), which is useful context, but offers no when-not guidance or routing to the other designation tools an agent might confuse this with. Usage is implied rather than stated.

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