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

No annotations are provided, so the description carries the full burden and does so well: it discloses coverage (England plus border stops), the gateway dependency and the exact failure behavior ('a deployment without the stops index answers a clear error'), and the attribution/licence obligation. That is richer than a typical read-only tool description.

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 and required inputs are front-loaded in the first two sentences, and each sentence carries real information. It is dense to the point of enumerating every returned field even though an output schema exists, which is the one place words could be spared.

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 4-parameter lookup with an output schema, the description covers everything an agent needs: input contract, mode and geographic coverage, error posture, downstream chaining, and display obligations. Nothing material is left to inference.

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% and the schema already spells out WGS84, the 1-to-50 limit and default 10, and the radius default 500, so the description's parameter text is largely a restatement. It adds the tighter '1 to 50' bound for limit versus the schema's declared maximum of 255, which is informative but also a minor inconsistency.

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 ('bus and coach stops near a point, nearest first') plus geography and mode scope, which cleanly separates it from nearby_places and next_departures in the sibling list. An agent can tell what it returns without opening the 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?

Gives the invocation condition (pass lat/lon), the exclusions (rail, tram, metro, ferry not included) and a chaining instruction (pass the returned id to next_departures). It never names a sibling as the alternative for the excluded modes, so it stops just short of full when/when-not/alternatives guidance.

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