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

Annotations already declare readOnlyHint=true and openWorldHint=false, so the description's job is to add operational detail — which it does: a hard 48-hour lookback for departures, ETA ordering for en-route ships, and the fact that output mirrors the Shiptrail page. It stops short of stating data freshness/latency or whether boards can be empty, which are the remaining behavioral unknowns.

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?

Two sentences, front-loaded with the resource and its two boards, with no filler. The first sentence is long and parenthetical, which slightly taxes scanning, but every clause (time windows, ordering, key) earns its place.

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?

For a two-parameter read tool with an output schema, the description covers scope, ordering, time window, per-list row semantics, and how to use the returned MMSI. Nothing an agent needs to invoke it correctly or interpret the result is missing.

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%, including the LOCODE pattern/example and the limit range plus its per-list meaning, so the schema already carries parameter semantics. The description only reinforces 'by UN/LOCODE' and the existence of two lists; it adds no format or edge-case detail beyond the schema, so baseline 3 applies.

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 the exact resource ('A port's Arrivals board ... and Departures board'), the lookup key ('by UN/LOCODE'), and the contents of each board (ships in port now, en route by ETA, departed in last 48 hours). It is clearly a port-detail fetch rather than a port search, and it explicitly points to get_ship for follow-up, so an agent can separate it from search_ports and get_ship without opening a 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 context for use is clear: you need a UN/LOCODE and want live port traffic, and the closing sentence tells the agent how to chain into get_ship via the MMSI. There is no explicit when-not-to-use or a named alternative for locating a LOCODE (presumably search_ports), which keeps it below a 5.

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