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

Annotations already declare readOnly, idempotent, openWorld, and non-destructive, so safety is covered. The description adds genuinely non-obvious operational context absent from annotations: a free-sample-per-day quota followed by $0.005 USDC per call via x402. It does not, however, discuss point-resolution behavior (lat/lng vs postcode) or rate specifics beyond pricing.

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?

Purpose is front-loaded in the opening clause, with the designation list and the pricing caveat following. The 20-item enumeration is long but earns its place by defining coverage scope; still, it is dense and slightly unwieldy as a single run-on sentence.

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?

For a wide aggregate tool with an output schema present, the description adequately covers scope (which designations), aggregation benefit, and cost model, so the agent needn't see return formats. Minor gaps remain around point-vs-postcode resolution and how sparse or verbose results may be, but nothing critical is missing.

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, and include_ended. The description adds no parameter-level guidance (e.g., precedence between postcode and lat/lng, or that include_ended surfaces revoked designations). Baseline 3 applies when the schema does the heavy lifting.

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 and resource ('Every published planning and environmental designation at a point in one call') and enumerates the exact designation types covered. This cleanly distinguishes it from the ~25 single-designation siblings like conservation-area, listed-building, and flood-zone, which return one type each. An agent can tell this is the aggregate tool without opening any 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?

The phrase 'in one call' clearly signals the use case: fetch the full designation set for a point rather than making many individual calls. However, it never explicitly tells the agent when NOT to use it or names the single-type siblings as the alternative for narrower queries. Context is clear but exclusions are absent.

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