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 new behavior: default 3 km radius, a hard 15 km cap, nearest-first ordering, and the pricing model (free within daily allowance, then $0.002 USDC per call via x402). Only the mechanics of the x402 payment flow are left unstated.

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?

A single front-loaded sentence packs radius defaults and limits, ordering, optional phase filtering, and cost into one line with no wasted words.

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, so return values need no explanation, and annotations cover safety; the description covers scope, constraints, ordering and cost. Minor gaps remain around error behavior for invalid postcodes and how the paid tier is actually invoked.

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, but the description adds meaning beyond the schema by disclosing the 15 km maximum on radius_km and the nearest-first ordering, which is not captured anywhere in the parameter definitions.

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 (find/list), resource (schools), and scope (within a radius of a postcode, nearest first), which cleanly separates it from siblings schools__search and schools__school. An agent can pick this 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 radius/ordering/phase phrasing implies the use case (proximity lookup filtered by phase), but there is no explicit statement of when to prefer this over schools__search or schools__school. Usage is inferable but not spelled out.

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