Next departures from a stop

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

With no annotations, the description carries the burden of disclosing behavior. It does so by mentioning real-time delays, internal stop-name lookup, and the candidate-list response when multiple stops match. This goes beyond the schema's parameter definitions, though it does not cover all edge cases (e.g., invalid inputs, no departures found).

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 concise sentences, each adding value: purpose, input options, and ambiguity handling. No fluff or repetition of schema info. The description is front-loaded with the primary function and scales well.

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?

Given the absence of an output schema, the description does not specify the structure of returned departures (e.g., fields like line, time, delay), which is a notable gap. It also omits error-handling behavior. The core purpose is clear, but the lack of return-format details makes it only moderately complete.

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%, so the baseline is 3. The description adds context about the OR relationship between stopId and stopName and the disambiguation behavior, but it does not add meaningfully to the numberOfDepartures parameter beyond what the schema already states. Thus, it slightly enhances but does not fully compensate beyond the baseline.

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 ('next departures from a Helsinki public-transport stop'), clearly distinguishing it from sibling tools like geocode or plan_journey. The scope is precise (Helsinki transit, real-time delays), leaving no ambiguity about what the tool does.

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 provides clear context on when to use this tool (to obtain departures from a stop) and explains the two accepted input modes, including a note about ambiguity resolution. However, it does not explicitly state when not to use it or mention alternatives (e.g., use plan_journey for route planning), so it falls short of a 5.

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