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

readOnlyHint=true and openWorldHint=true already establish this as a safe external read, so the bar is lower, and the description adds real value on top: the free 7-day window versus the paid 90-day window via Coast Map Pass, and that results are returned in station-local time. It does not disclose pagination, error behavior for out-of-range stations, or what happens when a station has no predictions.

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 compact sentences with the core purpose front-loaded and the access-tier constraint second; 'in local time' is a high-value detail that earns its place. No filler or restatement of the name.

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 no output schema, the description carries the return-value burden and does so adequately by naming the three event types (slack, max flood, max ebb) plus speeds and local time. It is slightly thin on how the four optional location/day inputs interact (station vs lat/lng fallback) and on what an empty or out-of-coverage result looks like.

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%, and the schema already documents lat/lng bounds, WGS84 convention, the days default of 2, the free/pass day limits, the 'from' format, and example station codes. The description adds nothing beyond the schema for any parameter, so the 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?

States a specific resource (slack water, maximum flood/ebb times and speeds at a current station) with the output units (local time), which is precise enough for an agent to distinguish it from tide_times. It never explicitly names the sibling tide_times or contrasts tidal currents with tidal heights, so differentiation is inferable rather than stated.

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 description gives entitlement conditions ('Up to 7 days free; longer with a Coast Map Pass key') but no when-to-use guidance relative to tide_times or when a lat/lng lookup is preferable to a station code. It also omits the implied prerequisite that station codes come from find_stations, leaving that inference to the schema.

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