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

Annotations only declare readOnlyHint; the description adds real behavioral context — that the service is free, and the precise rule under which a bare city name collapses to a single rail hub, including that a 'resolution' object exposes the rule and rejected alternatives. Doesn't describe rate limits or result ordering, but the disambiguation semantics are unusually well disclosed.

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?

Front-loaded with the cost note and the core verb, then builds to the resolution rule and the downstream usage hint. Three tight sentences with no filler; the leading 'Free.' is terse but earns its place as a cost signal.

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 no output schema, the description does the work of describing the return shape (stop_id plus a 'resolution' object) and the conditional resolution behavior. It leaves the ambiguity case implicit — what happens when multiple candidates exist — and says nothing about how 'limit' truncates results.

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?

The 'q' parameter is already documented in the schema, and the description adds genuine meaning by explaining how a bare city name resolves. However, 'limit' (default 5, max 20) is never mentioned, leaving half the parameters undocumented in both schema and description, so it does not compensate for the 50% coverage.

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 precise verb and resource: 'Resolve a station or city name to a stop_id.' The output artifact (stop_id) is named, and the tool is clearly distinguishable from siblings departures and plan_transfer, which consume rather than produce IDs.

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?

Explicitly tells the agent how to use the result: 'Use the returned stop_id as \'to\' in plan_transfer,' which establishes the chaining pattern. It does not state when not to use it or how it relates to departures, so it falls short of full when/when-not guidance.

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