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

Annotations already declare readOnlyHint and openWorldHint, so the safety profile is covered. The description adds valuable behavioral context beyond annotations: the search horizon of 'up to a month', the route scope of direct and one-change trains, and the operational constraint that it is 'EXPENSIVE' and 'limited to a few calls an hour.'

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?

Three sentences, each earning its place: core behavior, when to use, and cost warning with an alternative. It is front-loaded with the most important information and contains no filler.

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?

For a moderately complex tool with no output schema, the description covers what the tool returns, the search horizon, the journey types included, usage context, cost limits, and an alternative. It does not state what happens if no confirmed date exists within the month, but the phrase 'first date' and 'up to a month' make the behavior reasonably inferable.

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% and from/to/date already have clear descriptions like 'Origin station code' and 'The date to search forward FROM.' The description reinforces the date semantics with 'Search forward' but does not clarify the quota parameter or add detail 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 opens with a specific verb and resource: 'Search forward up to a month for the first date this route can actually be travelled with a confirmed berth.' It distinguishes the tool from siblings by explicitly scoping to 'direct trains and one-change journeys together' and by positioning it against check_train_options.

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 gives explicit when-to-use guidance: 'Use it when a traveller is flexible about WHEN and the date they asked for is waitlisted.' It also names the alternative check_train_options for the single-date case, leaving no ambiguity about when not to use it.

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