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

Annotations already declare readOnly, idempotent, openWorld and non-destructive, so safety is covered. The description adds behavioral value beyond them by disclosing what the response contains (live delays, platforms, transfers, cancellations) — important because there is no output schema. It says nothing about auth requirements, rate limits, or behavior when a station name is ambiguous.

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 short lines, front-loaded with the capability, then usage, then a parameter example. The example line is slightly redundant with the schema's own from/to descriptions, but it is cheap and immediately actionable.

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 7-parameter read-only lookup with no output schema, the description covers purpose, trigger, and the shape of the returned journey data — the pieces an agent needs. Remaining parameter details are handled by a fairly rich schema, and no output schema means return values legitimately fall to the description, which addresses them.

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 71%, so most parameters are already documented in the schema, including the language-agnostic station naming and the Belgian-time date/time semantics. The description's example supplies a concrete from/to format but adds nothing about results limits, time_is, or lang beyond 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?

States a specific verb+resource ('Train journeys between two Belgian stations') and enumerates the payload (times, delays, platforms, transfers, cancellations), so the agent knows exactly what it returns. It does not, however, name or contrast with the siblings (be_train_details, be_station_departures, be_rail_disturbances), leaving the A-to-B journey-planning distinction to inference.

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 'Use when' line gives a concrete triggering scenario with an example route (Brussels to Liège), which is a clear context statement. It offers no exclusions or alternative tools for adjacent cases like a single station's departure board or one train's details, so the agent must guess the boundary with siblings.

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