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

Annotations already cover the safety profile (destructiveHint=false, openWorldHint=false, idempotentHint=true), so the idempotent parenthetical is largely redundant. The real added value is "starts evaluating that campaign on its next sweep," which discloses non-obvious asynchronous timing that no annotation conveys. It omits whether re-attaching is a silent no-op or an error.

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 sentences, nothing wasted, with the core action stated first and the timing caveat second. No filler or restatement of the title beyond what is needed.

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 two-parameter, non-destructive mutation with no output schema, the description covers action, idempotency, and effect timing, which is most of what an agent needs. Only failure behavior (already attached, invalid ids) and the undocumented campaign_id remain unaddressed.

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 50%: `id` is documented as the auto-rule id, while `campaign_id` has no description at all. The description partly compensates by framing the operation as attaching a rule to a campaign, which makes the role of campaign_id inferable, but it adds no format, ownership, or constraint details.

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?

Uses a specific verb+resource ("Attach an auto rule to a campaign") that an agent can immediately separate from create_auto_rule, update_auto_rule, and detach_auto_rule without opening any schema. It stops short of explicitly naming those siblings, so it lands just under the top mark.

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 description implies the use case (linking an existing rule to a campaign) but never states when to prefer this over create_auto_rule or update_auto_rule, nor prerequisites such as the rule and campaign both already existing. The idempotency note is the only guidance on repeated invocation.

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