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

Annotations already declare readOnlyHint=false, idempotentHint=true, destructiveHint=false. The description goes beyond them with a required-permission note, the refusal behavior for classic polls, and the explicit side-effect guarantee 'never mails anyone' — valuable disambiguation in a suite containing send_invites. It could say more about what happens to an already-present date, but the additions are substantive.

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?

Three sentences, front-loaded with the core action and then the constraints. The first sentence is long and packs several rules into one em-dash chain, but every clause carries distinct information and nothing is 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?

With an output schema present, the description does not need to describe return values and instead covers what is missing elsewhere: permissions, side effects, per-event-type date validity, and the classic-poll refusal. An agent has everything needed to call this 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 coverage is only 50% (date carries no schema description), so the description does the heavy lifting: it explains both accepted forms (bare ISO string vs. object) and the per-event-type validity of daypart, startTime and endTime — a constraint the JSON schema cannot express. That is exactly the compensation low-coverage schemas need.

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+resource ('Adds one candidate date') and precisely scopes the target: a draft_ id from create_event or a live id from list_events/get_event. It also enumerates the two accepted date shapes, so an agent knows exactly what this tool does relative to siblings like set_date_time or remove_dates.

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 concrete usage conditions: dayparts work on any event, exact start/end times only on an autopilot event or draft, and an exact time on a classic share-link poll is refused. It does not explicitly contrast with set_date_time, so the routing is implied rather than spelled out, but the when/when-not rules are strong.

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