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

Annotations already declare non-read-only, idempotent and destructive, so the description's real contribution is the non-obvious hold-clamping rule ('a time sooner than the hold is moved to the end of the hold'), which materially changes what value ends up being used. It still does not explain why the tool is flagged destructive or what happens for non-queued/other-user IDs, leaving a gap against the destructiveHint.

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?

Two tight sentences with zero waste: purpose first, then the one behavioral caveat that changes agent behavior. Nothing is repeated from the schema or annotations.

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 and annotations covering the safety profile, the description supplies the scope and the hold rule needed to call it correctly. It could still say what an invalid/non-queued ID returns, but no critical calling information 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%, so baseline would be 3, but the description adds real constraint on the 'id' parameter: the target must be one of the current user's queued emails. The 'scheduled_for' parameter's clamping behavior is also described, going beyond the schema's bare 'ISO 8601 datetime to send at.'

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 ('Change when ... queued emails is sent') and scopes it to 'the current user's' queue, which separates it from draft-editing siblings like update-email-draft-tool. It never names the adjacent tools (cancel-email-tool, retry-email-tool) explicitly, so differentiation is implied by scope rather than stated.

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?

Use is implied by 'queued emails' – the agent can infer this applies only to emails already scheduled, not drafts or already-sent mail. However, no explicit when-to-use/when-not conditions or redirects to cancel-email-tool or retry-email-tool are given, so the agent must infer the boundaries.

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