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

Annotations already cover the safety profile (readOnlyHint, idempotentHint, destructiveHint=false), so the bar is lower, and the description adds genuinely useful behavioural context: a free daily allowance followed by $0.002 USDC per call via x402. That cost/payment model is not derivable from annotations or schema. It does not mention rate ceilings or the boundary cap on geometry, so it stops short of a 5.

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 sentences, front-loaded with the resource and coverage semantics, then input modes, then cost. No filler and nothing redundant.

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 present the description need not describe return values, and annotations cover safety. Purpose, input modes and the payment model are all present, leaving only minor gaps such as geometry capping behaviour and the point-only scope.

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 the schema already documents lat, lng, postcode, geometry and include_ended, making 3 the baseline. The description mirrors the postcode-or-lat/lng choice but adds nothing about the geometry or include_ended flags beyond what the schema states.

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 states a specific resource ('Registered historic battlefields') and its spatial semantics ('covering a point'), which uniquely separates it from the other uk-planning designation tools such as green-belt, sssi or scheduled-monument. An agent can tell exactly what this returns without opening the 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?

It tells the agent how to invoke the tool ('By UK postcode or lat/lng') and that pricing applies after a free allowance, but never states when to prefer this dataset over neighbouring designation tools or what prerequisites exist. Usage is implied by the resource name rather than explicitly guided.

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