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

Annotations already declare readOnlyHint and idempotentHint, so the safety profile is clear. The description adds behavioral context: 'live positions', 'within 1 km', and 'all transit vehicles' indicating no filtering, plus the WGS84 coordinate requirement. This is more than the minimum needed given the annotations, though no rate limits or error behavior are 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?

Three sentences, front-loaded with purpose, then usage guidance and coordinate requirement. Every sentence earns its place with no filler or redundancy.

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 an output schema present, the description does not need to explain return values. It covers purpose, intended use cases, alternatives, and a prerequisite for stop-name-only queries. It fully equips an agent to decide when and how to invoke the tool.

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 100%, so the schema already documents latitude/longitude with WGS84, ranges, and examples. The description repeats the WGS84 requirement and adds the 1 km radius constant, but does not add meaningful parameter-specific semantics beyond what the schema provides. 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?

The description opens with a specific verb+resource+scope: 'Returns live positions for all transit vehicles within 1 km of given coordinates.' This clearly distinguishes it from siblings like get_route_realtime, which is route-specific, and get_stops_around_location, which focuses on stops.

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?

Explicit when-to-use guidance: 'Use when the user asks "what transport is near me?" or wants a live map of all vehicles around a location without knowing the route.' It also names an alternative: 'Prefer get_route_realtime when a specific route is already known' and suggests get_stops_around_location if only a stop name is available. This covers when, when-not, and alternatives.

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