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

Annotations already indicate read-only, idempotent, and non-destructive behavior. The description adds valuable context beyond this: 'name resolution happens internally' and 'Live data: includes delays and cancellations for trains departing within 30 min.' These details enrich understanding without contradicting 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 three sentences, each serving a clear purpose: what the tool does, accepted inputs, and what it returns. It is front-loaded and free of redundancy or fluff.

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?

Although there is no output schema, the description lists key return fields (departure/arrival times, duration, transfers, trip IDs) and the live-data caveat. It does not mention pagination or the existence of get_more_connections, but the description is still substantial for a search tool with this complexity.

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%, with detailed descriptions for each parameter. The main description does not add significant parameter-level meaning beyond what the schema already provides (e.g., station names/IDs are already mentioned in the schema). Baseline 3 is appropriate.

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: 'Find train connections between two Swiss stations.' It uses a specific verb and resource, and distinguishes itself from siblings like search_stations (which finds stations) and get_prices/get_trip_details (which are downstream).

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 positions this as the entry point for schedule queries, noting it returns 'trip IDs for downstream pricing/details/ticket calls.' This implies when to use it relative to siblings, but it does not explicitly mention alternatives or when-not-to-use, so it falls just 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.