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

Annotations already declare readOnly, idempotent, openWorld and non-destructive, so the safety profile is covered. The description adds meaningful behavior beyond them: arrivals are live from the agency, while schedule data is broken out per line/direction across weekdays, Saturday and Sunday. No mention of rate limits, auth, or failure behavior, which keeps it from a 5.

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?

Purpose is front-loaded in the first sentence, followed by input guidance and then the return shape. The parenthetical enumerations are dense but each carries information the agent needs; there is 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?

With no output schema, the description takes on the burden of describing returns and does so explicitly for `station`, `arrivals` and `schedule`. Both required params are covered and the attribute list is documented, leaving only edge cases like invalid stations or pagination unspecified.

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%, so the baseline is 3, but the description adds real meaning: it enumerates the accepted city slugs (nyc, boston, bay-area, chicago, london) that the schema only exemplifies with 'nyc'. It also clarifies that `station` accepts either an id or a fuzzy name, clarifying the schema's 'id or name' hint.

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 ('Next arrivals and the timetable at a public transit station') and immediately names both inputs, so the agent knows exactly what it retrieves. It also implicitly distinguishes itself from the sibling nichedb_transit_city by pointing there for station ids.

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?

Gives clear usage context: supply `city` and `station`, and explicitly routes the agent to transit_city when it needs a station id, with a name-matching fallback. It does not state when-not-to-use or what happens when a city/station is invalid, but for a single-purpose lookup the routing guidance is solid.

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