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

Annotations already declare readOnlyHint=true and idempotentHint=true, lowering the bar. The description adds context beyond these: what data is returned (free/taken swim numbers, capacities, venue-specific rules, map URL) and the behavioral rule that single-swim requests at Golden Carp Lake must not be silently expanded. The 'never silently expand' instructions describe agent behavior rather than tool mechanics, but they still add operational context that complements the read-only annotation. No contradiction with annotations.

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?

At roughly 103 words across six sentences, the description is long but justified by the complexity of the Golden Carp Lake special case and downstream routing. It is front-loaded: core purpose first, then return values, then special-case rules, then general guidance. Every sentence earns its place, though the middle could arguably be tightened without losing the critical prohibitions.

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?

Given five parameters, no output schema, and the special Golden Carp Lake logic, the description is thorough: it states what is checked, what is returned, venue-specific handling, and downstream tool routing. The only gap is absence of explicit output-format details (no output schema exists to carry that burden), but the enumerated return types (free/taken numbers, capacities, rules, map URL) give the agent a solid model of the result. Sufficient for correct invocation.

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%, so the baseline is 3 and the schema already documents all five parameters with individual descriptions. The description reinforces two of them ('specific Saturday date' maps to date, 'actual party' maps to anglers), and it mentions accommodation_ids and booking_options as downstream values rather than this tool's parameters. This adds minor reinforcement but no new semantic detail beyond what the schema provides, so the baseline 3 is appropriate.

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 and resource: 'Check swim and accommodation availability for a venue on a specific Saturday date and actual party,' and lists concrete outputs (free/taken swim numbers, capacities, venue-specific rules, map URL). It distinguishes itself from list_crossings and list_venues by content, though it doesn't explicitly contrast with venues_available_on_date, a sibling with potentially overlapping scope. A clear purpose overall, but sibling differentiation is implicit rather than explicit.

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 provides exceptionally detailed usage direction: it names the Golden Carp Lake special case (four fixed booking_options, never individual swims), prescribes the exact flow (explain package, obtain acceptance before passing booking_option to get_quote, list_crossings, or prepare_booking), and states explicit prohibitions ('Never silently expand a single-swim request or increase the party to package capacity'). It also covers general venues ('pass chosen swims and accommodation_ids, or allow suitable free defaults') and flags that choices affect price, so the final selection must be quoted. This is proactive, alternative-routing guidance that leaves little to inference.

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