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

Annotations already declare readOnlyHint=true, idempotentHint=true, and destructiveHint=false, so the safety profile is covered. The description adds substantial behavioral detail beyond that: no auth required, source data provider (iRail SNCB/NMBS Belgium), and a precise list of response contents including departure status per stop. This paints a full picture of what the agent can expect from the call.

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 carrying distinct value: what it does, how to get the required id, and access/data notes. It is front-loaded with the core function and avoids redundancy. Every sentence earns its place with zero 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?

Given that all three parameters are fully documented in the schema, an output schema exists, and annotations cover safety and idempotency, the description is complete. It explains the key prerequisite (train ID source) and authentication status, leaving no critical gap for an agent to 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 every parameter already carries a descriptive comment, including the id's format and origin ('Obtain from liveboard or connections response'). The description slightly reinforces the id source but adds no new parameter-level meaning beyond what the schema conveys. Baseline 3 applies because 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?

The description opens with a specific verb and resource: 'Get the complete stop schedule for a specific Belgian train.' It enumerates the exact data points returned (scheduled times, delays, platforms, occupancy, departed status), making the tool's function unmistakable. It also names the sibling tools that provide train IDs, distinctly positioning this tool as the schedule-lookup follow-up to liveboard and connections.

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 establishes the prerequisite: 'Train IDs are returned by the liveboard and connections tools.' This tells an agent when this tool is appropriate (when it already has a train ID) without explicitly naming alternatives or stating when not to use it. There is clear context but no direct exclusion of sibling tools, fitting the 'clear context, no exclusions' level.

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