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

Annotations already declare readOnlyHint, idempotentHint and non-destructive behavior, so the bar is lower. The description adds real context beyond them: default window of ±31 days, a hard 366-day limit, and that all slot bounds and dayStart/dayEnd are interpreted in the user's timezone.

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 dense sentences, front-loaded with the purpose before constraints. Nothing is padding, though the parameter sentences are somewhat list-like and could be tightened.

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?

An output schema exists, so return format need not be described. All five parameters, their defaults, the window cap, and the timezone model are covered, leaving only the absence of routing guidance to siblings as a gap.

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 100%, so the schema already documents every parameter including defaults, ranges, and inclusive-date semantics. The description largely restates those (ISO 8601, default 30, range 5–1440) and adds only the timezone framing, so 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 verb and resource: 'Find unoccupied time windows in the authenticated user calendar.' This is clearly distinct from search_events or find_conflicts by implication, but the description never names those siblings explicitly to reinforce the distinction.

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 defaults (±31 days, duration 30) and the 366-day cap imply when the tool is applicable, but there is no explicit when-to-use/when-not guidance or reference to alternatives such as find_conflicts. Usage is inferable rather than stated.

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