Night trains / sleepers

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

Annotations already declare readOnlyHint and idempotentHint, so the description does not need to cover safety. It adds behavioral context: results are sorted by renown, city filter affects endpoints, and output includes a URL when available. This goes beyond annotations without contradicting them.

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 two sentences, front-loading the core functionality in the first sentence and usage guidance in the second. Every word contributes to understanding, with no redundancy.

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?

Given the tool's simplicity (single optional parameter, no output schema, clear annotations), the description covers purpose, filtering, output hints, and usage guidance. It is fully sufficient for an agent to select and invoke the tool correctly.

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 the parameter 'city' is already described in the schema. The description reinforces that the filter matches route endpoints and adds details like accent-insensitivity and that it filters for routes starting or ending in the city, adding semantic value beyond the schema.

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 explicitly states the tool returns sleeper routes sorted by renown, with optional city filtering and inclusion of a per-city guide URL. It distinguishes itself from siblings by specifying its use case for overnight/sleeper questions and pointing to alternatives like city_pair and search_routes.

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 clearly states when to use this tool ('Use for overnight and sleeper questions') and when to use alternatives ('city_pair for concrete A-to-B times; search_routes for other route categories'). This provides explicit guidance on selection.

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