search_fareCalculate fares between two stations on Tokyo Metro or Toei lines using ODPT data, returning the fare directly and supporting Japanese, English, or Chinese responses.
🚃 運賃検索 - 2駅間の運賃をODPTデータから検索します（東京メトロ・都営対応）。サーバー内で運賃を直接返します。language（ja/en/zh）指定で応答言語を強制可能。
| Name | Required | Description | Default |
|---|---|---|---|
| to | Yes | 到着駅 | |
| from | Yes | 出発駅 | |
| language | No | 応答言語の強制指定（省略時は駅名から自動判定） |
Changes observed during successful MCP inspections.
v2.58.7Input schema / $schemaAdded value: +"http://json-schema.org/draft-07/schema#"Input schema / additionalPropertiesAdded value: +falseInput schema / properties / languageAdded value: +{
+ "description": "応答言語の強制指定（省略時は駅名から自動判定）",
+ "enum": [
+ "ja",
+ "en",
+ "zh"
+ ],
+ "type": "string"
+}v1.0.0Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
Annotations already declare readOnly, idempotent, openWorld and non-destructive, so safety is covered. The description adds that the fare is returned directly server-side (no external redirect) and that the response language can be forced, which is modest but useful extra context beyond the structured fields.
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?
Compact and front-loaded: the emoji-prefixed title, the core action, the scope, and the language hint in essentially one dense sentence. No wasted phrasing, though the Christma-tree structure packs several clauses together.
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?
With no output schema, the description correctly notes that the fare is returned directly, and it discloses the operator restriction and language handling. An agent has enough to call it correctly, though it does not mention error behaviour for out-of-coverage stations.
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 all three parameters are documented in the schema itself, including the auto-detection fallback for language. The description repeats the language-forcing behavior rather than extending it, so the schema 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?
States a specific verb (search) and resource (fare between two stations), plus the data source (ODPT) and supported operators (Tokyo Metro/Toei). It is clearly distinct from siblings like search_route or get_timetable, though it names no sibling explicitly.
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 implied by the purpose, and the operator restriction (Tokyo Metro/Toei) quietly signals a coverage boundary, but there is no explicit when-to-use guidance, no when-not, and no pointer to an alternative tool for other operators or route planning.
Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.