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

Annotations already establish read-only, non-destructive, closed-world behavior, so the bar is lower; the description goes beyond them by disclosing the blocking rules ('Declined, cancelled and free events do not block time; all-day events block only when marked busy') and the working-hours/time-zone assumption. It still omits whether disabled calendars or missing permissions affect results.

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?

Two compact sentences, front-loaded with the core semantics (what a slot is and the duration parameter) before the blocking rules and defaults. Every clause carries information the schema does not.

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, and the description covers the compute rules, time zone, and defaults well. Gaps remain around sibling disambiguation and the unexplained calendar/category/limit parameters, but the core call semantics are complete.

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 carries the full burden, and it does explain duration_minutes, working_hours, days, and the start/end defaults and limit-per-day cap. However, calendar, category, and the numeric 'limit' parameter get no explanation at all, leaving several of the eight parameters semantically opaque.

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 ('Open slots of duration_minutes across the enabled calendars') with scope modifiers, making it clear this computes availability rather than listing events. It does not, however, distinguish itself from the sibling 'show_free_time', which an agent could easily confuse with it.

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 supplies useful default behavior ('now to 5 days ahead, at most 2 slots per day') that implies normal usage, but it never says when to prefer this tool over alternatives such as show_free_time, list_events, or propose_event. Usage context is implied rather than stated.

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