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

Goes well beyond the readOnly/idempotent/openWorld annotations: it discloses the API-key requirement and exact header format, plan-dependent history depth, credit cost (1 per vessel-day), rate limiting, the 24-hour delay on recent data for plans without live data, a 200-point cap per call, and the row shape returned. It also explains that missing points may reflect undelivered source days via sources_through/pending_days rather than vessel absence — a genuinely important behavioral caveat.

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?

Front-loaded with the core purpose, then constraints, then return semantics — a sensible order. The prose is dense with long parenthetical clauses (auth, resolution, credits) that could be split for scanability, but every sentence carries operative information.

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?

There is no output schema, and the description compensates fully by describing the returned row format ([time, lat, lon, speed_kn, course_deg]) and the sources_through/pending_days metadata. Auth, limits, cost, and data-freshness caveats are all covered, so an agent has everything needed to call it correctly.

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; the description earns above that by adding the hard limits tied to each resolution value and the 200-point-per-call ceiling, which constrain how an agent should set the range and resolution. mmsi and from/to are left to the schema, which already documents them adequately.

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 — where a ship has been between two times — plus the data source (AIS Trail archive). It is clearly distinguishable from siblings like vessel_events, port_calls, or get_vessel, which return events, port visits, or current/static data rather than a positional track.

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 concrete selection guidance for the resolution parameter (raw up to 24 h, 1m up to 7 days, 1h up to 366 days) and an explicit exclusion: clients that cannot add HTTP headers (OAuth-only web connectors) cannot use this tool. It does not name sibling tools as alternatives for narrower questions, so it stops short of a full when/when-not map.

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