Ferry positions

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

Annotations already cover read-only and open-world safety, and the description adds real value beyond them: the data source (AIS), the caveat that names are as broadcast and often English (which explains failed keyword searches), and that positions are not route-bound. It does not mention freshness/update cadence, which matters for a 'right now' claim.

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?

A compact, front-loaded paragraph: capability first, then the caveats, then examples. Every sentence carries information, though the closing example sentence largely duplicates schema examples and could be trimmed.

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 seven optional parameters and no output schema, the description usefully enumerates the returned fields and pins the geographic scope (Taiwan). The main remaining gap is the no-argument behavior — it never says what an unfiltered call returns beyond the schema default limit of 20 — and that lat/lon must be supplied together.

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 description coverage is 100%, so every parameter is already documented with ranges, defaults and examples; the baseline is 3. The description restates the three search modes and repeats example values (小琉球, TAIMA) already present in the schema, without explaining whether port/keyword/lat-lon are mutually exclusive or how radiusKm applies to each.

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 resource and scope: live AIS positions of ferries/passenger vessels around Taiwan, with the returned fields enumerated (position, speed, course, status, nearest port). It implicitly separates itself from ferry_timetable/ferry_live_board by noting positions are not tied to routes, but it never names the sibling it should be preferred over.

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?

"Search by vessel name, near a port, or near a point" conveys the three invocation modes, but gives no explicit when-to-use/when-not guidance and never points to ferry_live_board or ferry_timetable as the alternative for schedules or arrivals. The agent must infer the routing decision from the field list.

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