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

Annotations provide no behavioral hints, so the description carries that burden. It discloses the pairwise overlap behavior, collision minutes, whole-day event separation, calendar scope default, and a 31-day free bound. The phrase 'Free: 31 days' is a bit cryptic but still adds behavioral context. No contradiction with annotations.

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 short sentences, each carrying real information and no filler. The core definition is front-loaded, and the sibling distinction and edge-case handling are placed after the main purpose, which is an ideal structure.

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 tool with no output schema and no annotations, the description covers the main aspects an agent needs: what is returned conceptually, how whole-day events are handled, how calendar scoping works, and a usage boundary. The main gap is that the response format is not explicitly described and 'Free: 31 days' is ambiguous, but the description is still largely 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?

The schema already describes all three parameters at 100% coverage, so the baseline is 3. The description adds only mild clarification with 'unless you name one' for the calendar parameter. It does not meaningfully add to from/to beyond the cryptic '31 days' reference.

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?

The description states a specific verb and resource: 'Find double bookings' and defines precisely what counts as one—'every PAIR of timed events that overlap, with the minutes they collide.' It also distinguishes from free_busy by noting that free_busy 'shows gaps,' so the tool's purpose is unmistakable.

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 gives useful context for when to use the tool: overlap detection across calendars, with an optional calendar scoping. It explicitly names free_busy as the alternative for gaps. It does not enumerate exclusions versus every sibling, but the mention of free_busy is a clear enough routing signal.

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