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

Annotations already cover safety (readOnlyHint=true, destructiveHint=false), so the bar is lower; the description still adds real value by disclosing an API limitation (delivered campaigns are simply unavailable here), a plan/account requirement, and the underlying endpoint. It stops short of describing pagination or result-size behavior, which is the only remaining gap.

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?

Three short sentences, front-loaded with the scope constraint, then the alternative, then the precondition and endpoint. Nothing is repeated from the title and no sentence is filler.

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 no output schema, the description compensates by naming the returned fields, and it warns that delivered campaigns are unreachable before the agent wastes a call. For a zero-parameter read tool with annotations covering safety, nothing material 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?

The tool takes zero parameters, so there is nothing for the description to disambiguate — baseline 4 applies. The description correctly spends no space on phantom arguments and instead documents the output fields it will return.

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?

Specific verb (list) plus resource (campaigns) plus a hard scope qualifier: campaigns NOT yet delivered, explicitly defined as drafts and scheduled ones. It also enumerates the fields returned (id, name, subject, sender, schedule), so an agent knows exactly what this returns versus 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?

States the boundary condition outright: delivered campaigns are not listed by the API, and names the alternative (enginemailer_get_campaign_stats with a known id) for that case. It also adds a precondition ('Needs a paid account'), which is exactly the kind of when-to-use detail agents need.

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