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

Annotations already declare readOnly/idempotent/non-destructive/closed-world, so safety is covered. The description adds genuine behavioral content by enumerating exactly which factors the explanation reports (overlap events with their isBusy result, buffers, minimum notice, caps), which tells the agent what the diagnostic actually evaluates.

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?

A single front-loaded sentence with a colon-delimited list of return facets. Zero padding and the core purpose comes first. Slightly telegraphic, but every clause earns its place.

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 burden of describing what comes back, and it largely does by naming hours, overlapping events/isBusy, buffers, minimum notice, and caps. It omits the resolution ordering or shape of those results, but an agent has enough to call it correctly.

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 both parameters (time as ISO 8601 instant, event_type slug) are already fully documented in the schema. The description adds no syntax, format, or constraint detail beyond that, 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 (explain a time's bookability) and enumerates the diagnostic facets it reports: hours, overlapping events with isBusy, buffers, minimum notice, caps. An agent immediately knows what it gets back. It does not, however, distinguish itself from the sibling 'preview', which could plausibly cover similar ground.

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 'why a time is or is not bookable' framing implies a diagnostic/verification use case, but there is no explicit when-to-use statement, no prerequisites, and no pointer to the likely-overlapping sibling 'preview'. 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.