path_arrivals

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

Annotations declare readOnlyHint=true, so the safe-read nature is covered. The description adds useful behavioral context: it is 'real-time', returns specific data (station names, line info, projected arrival times, train status), and requires no API key. This goes beyond the annotation without contradicting it.

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?

The description is three sentences, each earning its place: the first states the core action, the second lists return contents, and the third provides geographic scope and access requirements. It is front-loaded, concise, and free of filler.

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 parameterless, read-only tool with no output schema, this description is complete: it covers what is returned, the geographic scope, real-time nature, and authentication requirements. An agent has all necessary information to invoke the tool 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?

The input schema has zero parameters, and the description appropriately states 'for all stations', clarifying that there is no filtering or input customization. With no parameters to document, the baseline is 4, and the description effectively communicates the no-input nature.

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 uses a specific verb ('Get') and resource ('real-time PATH train arrival times'), clearly distinguishing this from other transit tools by naming PATH and its service area (NY/NJ metro, Manhattan to Jersey City, Hoboken, Harrison, Newark). It also states what is returned, making the purpose unambiguous.

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 description gives clear context: it is for PATH trains, covers all stations, and requires no API key. While it does not explicitly mention alternatives or exclusions, the tool's scope is obvious given its name and content, so an agent can correctly decide when to use it over other transit tools.

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