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

With no annotations, the description carries the full burden. It discloses that it applies the saved filter and returns three numbers (base, exclusions, final total), making the behavior transparent. It doesn't explicitly state read-only, but 'ANTES de enviar' implies no side effects.

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 a single, well-structured sentence that leads with a user-oriented question, then provides a clear answer. Every word adds value, with no filler or repetition of the tool name.

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 one parameter and no output schema, the description is complete: it explains the purpose, timing, and the nature of the return value (counts). It doesn't describe exact JSON keys, but for a simple tool this is acceptable.

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?

There is only one parameter, campaign_id, with 0% schema description coverage. The description doesn't explicitly mention the parameter but implies it via context (the campaign whose audience is calculated). The phrase 'aplicando el filtro guardado' adds meaning about how the parameter is used, though it doesn't compensate fully for missing schema documentation.

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 a specific verb ('Devuelve') and resource ('destinatarios REALES') with a clear context ('ANTES de enviar'). It distinguishes itself from sibling tools like get_campaign_stats by focusing on pre-send audience size calculation.

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?

It explicitly says to use 'ANTES de enviar' (before sending), giving clear temporal usage context. No alternatives are named, but the context is sufficient to differentiate from post-send stats tools.

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