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

Beyond the readOnly/openWorld annotations, it discloses real operational traits: live data requires NJT credentials, bus live data is unavailable in v1.2, PATH needs no key, and all times are America/New_York. This is substantive context the annotations cannot convey, though it doesn't discuss pagination or what happens when a station 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?

It is front-loaded with the core action and then groups per-system behavior compactly. The trailing NOTE earns its place by preventing a plausible wrong assumption (that NJT has a subway), though the serviceability of the block format is slightly repetitive with the per-system lines.

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 an output schema present, return values need not be described, and the system/credential/timezone context is rich. The remaining gap is the three undocumented optional parameters (line, limit, towards), which leave filtering behavior underspecified for a tool with 0% schema description coverage.

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 0%, so the description must carry the parameter burden. It does explain 'station' (name or stop ID) and 'system' (three enumerated values with semantics), but 'line', 'limit', and 'towards' are left entirely undocumented, so the agent must guess at their format and filtering behavior.

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 names a specific verb+resource ("next departures from a station/stop") and immediately scopes it across three transit systems, making it clearly distinct from siblings like trip_between, service_alerts, and search_stations. An agent can identify the tool's role without opening the schema.

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 explicitly routes between system values: 'nj_transit' for rail/light rail with live-versus-scheduled behavior, 'nj_bus' for scheduled-only bus, and 'path' for live arrivals with no key. It even warns there is no NJ subway and directs subway-like use to 'path' or HBLR/NLR/River Line, which is exactly the when-to-use guidance an agent needs.

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