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

With annotations already declaring readOnly/idempotent, the description still adds substantial context: data is derived from schedule and charted route rather than live GPS/AIS, it is exact at port calls and estimated in transit, and times are port-local. This is precisely the kind of accuracy caveat an agent needs before presenting the result to a user.

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?

Content is front-loaded with the core answer and the accuracy caveat follows immediately. The first sentence is dense with three parenthetical cases but every clause carries information; nothing is redundant.

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?

No output schema exists, yet the description still tells the agent what comes back (upcoming stops, approximate coordinates, tracker and sailing links) and how reliable it is. That is complete for a single-parameter lookup.

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?

There is only one parameter ('ship') and the schema documents it fully at 100% coverage, including an example. The description adds no additional parameter meaning, so it sits at the baseline for well-covered schemas.

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 opens with a specific verb-phrase and resource ('Where a ship is right now') and then enumerates the three distinct states the tool resolves: in port, at sea, between sailings. This is unmistakably different from siblings like getShipProfile or searchCruises, so an agent can route to it without inspecting 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?

The scenario is clear — use this when you need the ship's current location and upcoming stops. There is no explicit when-not or named alternative, but for a single-purpose lookup tool the implied context is unambiguous.

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