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

Annotations already establish readOnlyHint=true and openWorldHint=true, so safety is covered. The description adds genuine context beyond them: the result is limited to bookable slots and policy and never exposes the raw calendar, slots are absolute ISO-8601 UTC instants, and timezone rendering depends on viewerTimeZone. It does not mention pagination or result-size limits.

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?

Four tight sentences, each earning its place: scope, exclusivity of return data, workflow placement, and timezone semantics. The most decision-relevant facts (what is returned, what is not) are front-loaded.

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: it names the two return components (bookable slots plus booking rules such as durations, minimum notice, advance horizon, buffers) and the instant format. Combined with the annotation-covered safety profile, nothing essential for correct invocation 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%, so the baseline is 3. The description goes further by explaining why viewerTimeZone should be the booker's own zone ('the booker should never have to do time-zone math') and that slots are absolute instants, adding rationale the schema does not carry.

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 ('Return the open meeting slots a Lucie Sync host offers, plus their booking rules') and explicitly scopes what is returned versus withheld ('never the host's raw calendar'). An agent can distinguish this read/reconnaissance tool from the booking siblings (book_meeting, book_group_meeting) 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 clear timing guidance — 'Use this to find a time before proposing one to the user' — which situates it in the workflow ahead of the booking tools. It does not explicitly name an alternative or state exclusions (e.g., when to prefer find_group_times for multi-party scheduling), so it stops short of a 5.

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