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

Annotations already declare readOnly, idempotent, non-destructive and openWorld, so safety is covered. The description adds the useful fact that results include live delay/cancellation data (real-time freshness), but says nothing about data source latency, caching, coverage limits, or auth needs for live feeds.

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?

Two compact lines plus one inline example; the returned-field list is front-loaded before the usage and example cues. Every sentence carries information and nothing is padded.

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?

With no output schema, the description responsibly enumerates the returned fields, and it supplies when-to-use plus an example. Only the unadvertised 'lang' switcher and 'results' bound remain uncovered, which are minor for a single-purpose lookup tool.

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 50%: only 'time' and 'station' carry descriptions, while 'lang' and 'results' are undocumented. The description compensates partially with the {"station":"Namur"} example and the note that station names work in any language, but it never mentions 'lang' or the results limit, so the gap is only partly closed.

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 and resource ('next train departures from one Belgian station') plus the exact payload fields returned (time, destination, platform, live delay, cancellations). This cleanly separates it from siblings like be_train_connections (journeys) and be_rail_disturbances (network issues) without needing their schemas.

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?

Explicit 'Use when: someone is at (or going to) a station and wants the next trains' gives a concrete selection context, and the example invocation anchors it. It does not name an alternative tool or state when NOT to use it (e.g. use be_train_connections for trip planning), so it stops 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.