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

Adds substantial context beyond annotations: irreversible send, locks the recipient list, progressive delivery, no recall of sent email, and a human-confirmation requirement. It also clarifies filtering against active subscribers and suppression of unsubscribed/suppressed addresses, which annotations alone (destructiveHint=true) would not convey.

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?

Six compact sentences, front-loaded with the irreversible warning and the scope behavior, then the required preview/confirm workflow, then delivery/progress tracking. No redundant or filler clauses.

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 destructive mutation with no output schema, the description covers the critical gaps: irreversibility, recipient-list locking, filtering semantics, pre-send preview, human confirmation, and progress tracking via get_campaign_stats. Nothing essential 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 description coverage is already 100%, so the baseline is 3. The description adds behavioral meaning: `to` restricts to active subscribers only, empty list is refused, and omit for the whole list. This goes beyond the schema's terse parameter text.

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 ('send a campaign') and immediately distinguishes scope: all active subscribers, or a restricted set via `to`. It also names the sibling preview_campaign_send for the pre-send step, so an agent can tell this apart from send_email and get_campaign_stats.

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?

Explicit when-to-use and a required pre-call workflow: 'First call preview_campaign_send with the same parameters, then ask the person for explicit confirmation'. Also states filtering behavior with the `to` parameter, leaving no inference to the agent.

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