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

Beyond the readOnlyHint and idempotentHint annotations, the description adds a key behavioral boundary: 'Timetable only — it says nothing about seats.' It also implies a focus on direct trains, which is extra contextual nuance. These details help an agent know what to expect without contradicting the annotations.

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 concise and well-structured: the first sentence states the core purpose, the second gives usage context, and the third clarifies a critical limitation. Every sentence earns its place with no redundancy, and the most important information is front-loaded.

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 and the description gives a solid high-level overview, but it does not describe the exact output format (e.g., a list of dates or a weekly pattern summary). It also leaves the 'days' parameter's meaning and default behavior unexplained, which is a gap given there's no output schema to rely on. An agent might be uncertain about what is returned and how to interpret the 'days' input.

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 75% (from, to, start_date have descriptions), so the baseline is 3. However, the description does not elaborate on the 'days' parameter, which lacks a schema description. The phrase 'span of dates' indirectly references start_date and days, but no explicit meaning is added. The description neither compensates for the missing days description nor enhances the existing ones.

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 states the tool's function: 'Day-by-day service over a span of dates for a station pair: which days have a direct train and which have none, plus the weekly pattern.' It specifies a concrete resource (service availability for a station pair) and a distinct behavior (day-level pattern) that separates it from sibling tools like train_schedule or next_confirmed_date.

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?

It provides explicit when-to-use guidance: 'Use this when somebody is flexible about when they travel, or asks "does it run on Sundays"' and a clear when-not: 'Timetable only — it says nothing about seats.' It does not name an alternative tool for seat checks, but the context is sufficient to route an agent appropriately.

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