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

Annotations already declare readOnlyHint=true, idempotentHint=true, destructiveHint=false and openWorldHint=true, so the safety profile is covered. The description adds that results are 'live' (real-time rather than scheduled) and that a single station is queried, but says nothing about data freshness/latency or what happens for an unrecognized station.

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 sentence with no filler, front-loaded with the core action and resource, followed by the mode scope and the optional filter. Nothing is wasted and nothing essential is buried.

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 a fully described 3-parameter schema, complete annotations and an output schema, the definition covers what an agent needs to invoke it. The only shortfall is that real-time data characteristics (refresh behavior, failure mode for ambiguous station names) are left unstated.

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 an output schema exists, so the schema already documents stop, limit and route with examples and bounds. The description only reinforces that route is optional and single-valued ('one route or line'), adding marginal value beyond the schema.

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 resource (live departures) scoped to one MBTA station and enumerates the covered modes (subway, Commuter Rail, bus, ferry), which is more than a restatement of the title. It is clearly a departure-board lookup rather than a journey planner, so an agent can separate it from plan_trip without opening the schema, though the sibling is never named.

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?

Usage is only implied: 'live departures at one MBTA station' signals real-time schedule lookups versus trip planning. There is no explicit statement of when to prefer this over plan_trip, nor any note about prerequisites such as needing an exact station name.

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