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

Annotations already cover read-only, idempotent, non-destructive and open-world behavior, so the bar is lower; the description still adds genuinely new context by disclosing the pricing model (free within the daily allowance, then $0.002 USDC per call via x402), which is not in the annotations or schema.

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?

Two compact sentences, front-loaded with the resource and output, followed by the input modes and the billing caveat. No sentence is filler.

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?

An output schema exists and the annotations carry the safety profile, so the description only needs to establish what is returned, the accepted inputs, and the cost. It does all three, though it is silent on behavior when the point falls outside any ward.

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 baseline is 3. The description reinforces the postcode-vs-lat/lng choice but adds nothing for geometry or include_ended; the include_ended parameter looks like a carry-over unrelated to wards.

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 (electoral ward for a point) and even names the returned field (ONS code), which is more than most siblings manage. It is clear within the planning family, but it does not distinguish itself from the near-identical uk-geography__ward sibling.

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?

'By UK postcode or lat/lng' is an input-mode instruction, not a when-to-use rule, and it duplicates what the schema already says. Nothing explains when to pick this over uk-geography__ward, uk-planning__parish or uk-planning__region, so the agent gets no routing help.

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