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

With readOnlyHint=true already covering the safety profile, the description adds real value beyond annotations: the return shape (per-account list of busy {start, end}), the free-by-omission semantics, and the default window. It doesn't mention auth/scope requirements, pagination, or rate limits, but the critical output behavior and its non-computation limitation are disclosed.

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 verb and resource. Every sentence earns its place: the primitive provenance aids routing, the return semantics set expectations, and the closing sentence prevents a common misuse (expecting computed slots). No filler.

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?

There is no output schema, so the description carries the return-value burden and does so ('each account's list of busy {start, end} periods ... anything not listed is free'). Combined with defaults and the explicit scope limitation, an agent has everything needed to call it and interpret the result.

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 all six parameters (tz, days, accounts, time_max, time_min, calendar_id) are already documented. The description restates the 'default primary' calendar and 'today + 7 days' window but adds no syntax or format detail beyond the schema, so the 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 ('Query busy periods across the user's Google Calendar accounts') and pins the underlying primitive (Calendar's freebusy.query). It distinguishes itself from list_calendar_events by returning busy {start, end} periods rather than events, and even names the suggest_time relation, so an agent can route to it without opening a 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 context — use it to obtain busy intervals, and 'anything not listed is free' establishes the interpretation rule. It explicitly warns 'This does NOT compute open slots itself', steering the agent to reason over the result. It stops short of naming a sibling alternative (e.g., list_calendar_events) to use instead when event detail is needed, so not quite a 5.

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