search_fare

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

With no annotations, the description carries the transparency burden. It discloses data source (ODPT), scope (Tokyo Metro/Toei), and a behavioral trait (returns fare directly without external Yahoo dependency). However, it omits details like output format, error handling, or exact station name requirements, leaving some behavioral aspects undisclosed.

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 a single, front-loaded sentence with an emoji for visual cue. It efficiently conveys purpose, data source, scope, and a key implementation detail without redundancy. Every phrase 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?

The tool is simple (2 params, no output schema), and the description covers the core function and constraints. However, since no output schema exists, it would benefit from describing the return format or potential error behavior. The mention that it 'returns the fare directly' hints at output but lacks detail, making completeness adequate but not thorough.

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% with each parameter described ('出発駅' for from, '到着駅' for to). The description's phrase '2駅間' adds minimal semantic value beyond the schema, confirming the two-station relationship. Baseline 3 applies since the schema carries the parameter documentation burden.

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 identifies the tool as a fare search ('運賃検索') between two stations, specifying the resource (fare) and scope (ODPT data, Tokyo Metro/Toei). It distinguishes itself from siblings like search_route by emphasizing direct server-side fare calculation without Yahoo dependency, making its unique purpose explicit.

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: use for looking up fares between two stations, with support for Tokyo Metro/Toei. However, it does not explicitly contrast with alternatives like search_route or get_station_info, and the mention of 'Yahoo dependency' is a benefit rather than a usage boundary. Guidance is implied rather than explicit.

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