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

Annotations already declare readOnlyHint, idempotentHint, openWorldHint and destructiveHint=false, so the safety profile is fully covered elsewhere. The description contributes only 'including service patterns' as return-content context, and with an output schema present there is little burden left on the prose.

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 short, front-loaded sentences with no filler; the capability comes first and the scope restriction second. Minor overlap between 'NYC Subway only' and the city enum keeps it from being maximally tight.

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 two-parameter lookup with rich annotations and a declared output schema, the description supplies purpose plus scope, which is nearly everything an agent needs. Only an explicit pointer to the sibling routes tools 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 coverage is 50%: routeId is well documented in the schema while city carries only an enum. 'NYC Subway only' reinforces the single-value city enum and the NYC-only routeId list, but the description adds no format or syntax detail beyond the schema. Baseline 3 is appropriate.

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 — 'Get detailed information about a transit route' — and adds the payload detail 'including service patterns'. The 'NYC Subway only' scoping separates it from the get_sfbay_routes and get_bus_routes siblings, though no sibling is named directly.

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 'NYC Subway only' clause implies the usage boundary and effectively rules out the SF Bay and bus siblings, but the description never names an alternative or states an explicit when-to-use condition. Usage is inferable rather than stated.

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