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

Annotations already declare readOnlyHint, idempotentHint, and destructiveHint=false, so the safety profile is known. The description adds useful context by describing it as a 'lightweight free/busy view' and enumerating returned fields, but it does not go further into authentication needs, rate limits, or edge-case behavior like empty calendars or timezone handling.

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?

The description is two focused sentences. The first sentence front-loads the core behavior and output fields, and the second adds practical use-case guidance. There is no filler or repetition of the schema.

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?

The tool is simple: one optional, well-documented parameter, a clear read-only operation, and a description that lists the main output fields (start, end, subject, all-day flag). Minor details like ordering or timezone are not specified, but they are unlikely to prevent correct invocation.

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% and the only parameter, days_ahead, is already documented with its type and default value (7). The description's 'next N days' phrasing aligns with the schema but does not add new semantics beyond it, so the baseline of 3 is appropriate.

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 ('Return') and a specific resource ('user's busy time windows from their Outlook / Microsoft 365 calendar over the next N days'). It also frames the tool as a 'lightweight free/busy view,' which distinguishes it from sibling tools like list_events or get_event that would return broader calendar event data.

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 explicitly says 'Use to find when the user is available or to identify scheduling conflicts before proposing a meeting time,' which gives a clear contextual trigger. It does not name alternatives or state when not to use it, so it stops short of a full 5.

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