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

Annotations only cover safety/idempotency, and the description adds substantial non-obvious behavior: autopilot charging on a draft at send, refusal on a live classic poll, immutability of a confirmed date, the write-permission requirement, and that no email is sent. It is close to complete, though it doesn't say what the response looks like or what happens to an existing daypart when an exact time is set.

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 primary action and its exclusivity rule are front-loaded, followed by routing, refusal, and side-effect details. Every sentence carries a distinct constraint, though the density of em-dash clauses makes it slightly harder to scan than a shorter equivalent.

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 5-parameter mutation tool with an output schema (so return shape needn't be described), the description covers prerequisites, alternative tools, refusal conditions, side effects, and the clearing semantics. Nothing needed to call it correctly is missing.

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% (baseline 3), but the description adds constraints the schema does not encode: exact start/end and daypart are mutually exclusive ('never both'), and omitting all three clears the time. That mutual-exclusivity rule is genuine value beyond the field descriptions.

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 precise verb+resource pair (set/clear the time on an existing date) and immediately scopes it against the sibling add_dates, which 'refuses a duplicate day'. An agent can route between set_date_time and add_dates without opening either 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?

Explicitly names the alternative and its limitation ('The one way to put a time on a date that is already there'), and states where the tool is refused (live classic/share-link poll, confirmed date on a live event). It also gives the clearing case: omit all three to revert to a plain day.

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