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

With no annotations provided, the description carries the full burden. It adds valuable behavioral context: returns the real recipient count and fails with HTTP 400 if any reference is missing instead of saving partially (atomicity). It does not disclose whether existing audience rules are overwritten, which is a minor gap, but the disclosed behaviors are significant and non-obvious.

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?

The description is three sentences long, each earning its place: purpose, return value/confirmation, and error behavior. It is front-loaded with the core function and avoids any filler or repetition.

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 tool with 6 parameters, no output schema, and no annotations, the description provides a solid high-level overview including purpose, output behavior, and error handling. However, it omits mention of include_tags (positive targeting) and tag_on_delivery side effects, which are covered only in schema param descriptions. Overall, it is reasonably complete for an agent to select and invoke the tool correctly.

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 83%, and param descriptions in the schema are already informative (e.g., 'nombre o UUID', 'manda a A menos los de B'). The tool description adds no additional parameter meaning beyond restating the exclusion concepts, so it does not elevate above the baseline for well-documented schemas.

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 clearly states the tool defines who receives an email and who does not, with specific exclusion criteria (tags, lists, previously received campaigns). It distinguishes from sibling get_campaign_audience by using the verb 'define' (set) and mentioning the return of the real recipient count, which is a unique behavioral feature.

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 usage before sending a campaign ('confirmar antes de enviar'), providing clear context for when to use it. However, it does not explicitly exclude alternatives or mention sibling tools like get_campaign_audience, so it lacks an explicit when-not-to-use statement.

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