Metro fares

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

Annotations only say read-only and open-world; the description adds what comes back (fare in NT$, broken out by passenger type, plus distance), which is meaningful since no output schema exists. It stops short of naming the passenger types or stating whether cross-system trips are supported.

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?

One compact sentence followed by a concrete example, front-loaded with the core purpose. 'with the distance' is slightly tacked on but nothing is wasted.

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 simple 3-parameter, read-only fare lookup with no output schema, the description covers purpose, currency, and the shape of the result. The remaining gap is which passenger types are returned and whether an unsupported station pair errors or returns null.

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% and already documents station name/ID formats and every system enum value. The description's example adds a concrete TRTC/台北車站/淡水 call pattern, which is mildly useful but largely restates schema conventions.

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 verb+resource: single-journey metro fares between two stations, with currency and per-passenger-type dimension. The 'metro' scope implicitly separates it from thsr_fare/tra_fare siblings, though it never names them.

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 by the worked example (system TRTC, from 台北車站, to 淡水). There is no explicit statement of when to choose this over thsr_fare or tra_fare, or any prerequisite such as both stations needing to be on the same system.

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