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

Annotations already cover the safety profile (readOnly, idempotent, non-destructive, closed-world), so the description's added value is declaring the returned metrics: send, open, and click counts. With no output schema present, that return-content disclosure is genuinely useful; it stops just short of describing pagination or result limits.

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?

A single sentence with no filler, leading with the resource scope and then the payload. Nothing is wasted and the most decision-relevant information comes first.

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 no-parameter read tool with rich annotations, the description covers what comes back (counts). The only gap is the absence of any scope caveat such as result limits or default ordering, which would matter since there is no output schema and no parameters to control them.

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?

The tool takes zero parameters, so per the rubric the baseline is 4. The description correctly implies no filtering input is needed, and the schema has nothing to document.

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 names a specific verb+resource ('email campaigns') and scopes it to the user's own campaigns, which separates it from the get_campaign sibling. However, it never explicitly contrasts itself with list_lists or get_campaign, so sibling differentiation is implied 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?

Usage is only implied: the zero-argument 'list' shape makes it fairly obvious when to reach for it, but there is no explicit when-to-use, no alternative named, and no statement of what it does not return (e.g., individual campaign details, which would route to get_campaign).

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