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

Annotations already establish this is a safe read, so the description wisely spends its budget elsewhere: it discloses the 90-day horizon, the Chicago-time 'already departed' cutoff, that null durationId means offered-but-not-bookable, and the harborIds departure restriction. These are behavioral traits the agent could not infer from readOnlyHint/destructiveHint.

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 contract and no filler sentences; every clause carries a rule. The later sentences are long and clause-dense (harbor rules), which costs some scannability, but 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?

For a 4-parameter read tool with no output schema, the description covers inputs, both response modes, the shape of each mode (dates, slots with offeredDurations), sentinel values, and the coupling to booking tools. Nothing an agent needs in order to call it correctly 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 0%, so the description must carry all four parameters — and it largely does: mutual exclusivity of captainSlug/boatId, the YYYY-MM-DD date format, and the date+durationHours pairing are all spelled out. It falls short only on the origin/format of boatId and captainSlug (both presumably from sibling lookups, which are not named here).

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 ('Check a captain's or boat's availability') and immediately distinguishes the two lookup modes (date list vs. time slots). It also names the downstream siblings that consume its output (get_quote, create_booking, create_boat_rental), so an agent can place it in the workflow without opening any 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?

Gives explicit input rules — 'Provide exactly one of captainSlug or boatId', omit date for the 90-day list, supply date plus durationHours for slots — and explains the failure case (past dates have no slots) and the harbor constraint that later blocks create_booking. That is genuinely when-to-use/when-not guidance with alternatives named.

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