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

Annotations already declare readOnlyHint=true and idempotentHint=true, so the safety profile is known. The description adds context about the output being 'live positions' and 'optimised for map rendering', which is useful beyond the annotations. It doesn't contradict annotations, and the lack of extra detail (e.g., pagination) is acceptable given the simple, read-only nature.

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 with the primary purpose first, followed by targeted usage guidance and a parameter requirement. No redundant information; each sentence earns its place.

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?

Simple tool with one parameter, output schema present, and strong annotations. The description covers purpose, use cases, alternatives, and a parameter hint, making it complete for an agent to select and invoke correctly.

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% with a clear description of route_name including examples. The description restates the requirement but adds no new parameter semantics beyond the schema. Baseline 3 applies because the schema already does the heavy lifting.

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 clearly states the tool returns live positions for all vehicles on a route, with a specific verb ('returns') and resource ('live positions'). It differentiates from siblings by mentioning 'optimised for map rendering' and explicitly contrasting with get_stop_realtime and get_route_static.

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?

Provides explicit when-to-use guidance with a concrete user query example ('where is my tram/bus right now?') and names alternative tools for different scenarios (get_stop_realtime, get_route_static). This is exemplary usage guidance.

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