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

Annotations already cover the safety profile (readOnly, idempotent, openWorld, non-destructive), so the description is free to add the less obvious facts it does add: the cost model (free within daily allowance, then $0.002 USDC via x402) and the conditional result ('if parished'). It stops short of saying what happens when a point is unparished.

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 purpose before the input methods and pricing. Nothing is padded or 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 annotations carrying safety and an output schema carrying the return shape, the description only needs to add purpose, inputs, cost and edge cases, which it mostly does. The one real gap is the unparished-result behavior and the meaning of the geometry/include_ended flags.

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, geometry, postcode and include_ended. The description only restates the postcode-vs-lat/lng choice and adds nothing about the geometry or include_ended parameters, so baseline 3 applies.

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 (the civil parish) and the spatial scope (for a point), plus the accepted input methods. It does not, however, distinguish itself from the near-identical sibling uk-geography__parish, leaving the agent to guess which parish tool to pick.

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?

Usage is implied rather than stated: 'By UK postcode or lat/lng' tells the agent what inputs work, and 'if parished' hints at the coverage limit. There is no explicit when-to-use guidance, no exclusions, and no routing to the sibling parish/geography tools.

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