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

Goes well past the annotations (which only declare readOnly/non-destructive/closed-world) by disclosing negative output behavior ('no event titles, sources, notes or participant details') and, crucially, the external-calendar coverage semantics — 'included', 'not_connected', staleness reasons, and the caveat that only external_included=true means full coverage. That staleness contract is the kind of thing an agent could not guess from any structured field.

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, front-loaded with the operation and scope, then output exclusions, then the coverage contract. Dense without filler; the quoted flag values cost a little readability but carry real information.

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 three-parameter, zero-required read tool with annotations and no output schema, this covers what is returned, what is deliberately omitted, and how to interpret per-user coverage. Only edge-case behavior (unknown user_ids, empty result handling) is left unaddressed.

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 coverage is only 33% (user_ids and days have no descriptions), and the description compensates meaningfully: it pins user_ids to active members of the caller's current workspace, characterizes days as local calendar days bounded at 1–7, and reinforces the ten-user cap. It still does not say what happens to invalid or non-member ids.

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 concrete verb ('Read') and precise resource ('busy intervals') with explicit scope: up to ten active members in the caller's current workspace, one to seven local calendar days. It implicitly separates itself from agenda/free-slot siblings by stressing busy-only, title-less output, but never names an alternative.

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?

Usage is implied rather than stated: the description makes clear this is for raw busy-block reads, not scheduling, but there is no explicit when-to-use guidance and no pointer to planner_free_slots or planner_suggest_slots for the scheduling case.

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