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 non-obvious operational context the annotations cannot convey: the point lookup is free within a daily allowance and then costs $0.002 USDC via x402, which materially affects how an agent should batch or ration calls. It stops short of describing boundary-capping behavior for the geometry flag.

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 tight sentences with zero filler: output identity first, accepted inputs second, cost model last. Every clause earns its place and nothing is buried.

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, return values need no narration, and the annotations carry the safety profile. What remains is a real gap: no hint of what distinguishes this tool from the parallel geography/planning siblings, which for a directory of 80+ near-duplicate tools is the one thing an agent most needs.

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 every one of the 5 parameters is already documented in the schema, and the baseline is 3. The description restates the postcode-or-lat/lng choice that the schema already encodes, adding no new syntax, format or constraint detail beyond it.

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 verb/resource pair — 'the local authority district for a point' — plus the added payload ('with its ONS code'), so the agent knows exactly what comes back. However it never distinguishes itself from near-identical siblings such as uk-geography__local-authority or uk-planning__planning-authority, leaving the agent to guess which one to call.

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?

The phrase 'By UK postcode or lat/lng' does tell the agent which input modes are accepted, which is useful context. But there is no when-to-use guidance and no exclusion or routing against the many overlapping geographic siblings, so selection is left to inference.

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