Buscar factura por número

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

Annotations already declare readOnlyHint=true, so the safety profile is covered. The description adds useful scope information (searches across all periods, exact-match only), but says nothing about whether a no-match returns an empty list or an error, or whether multiple periods can yield multiple results.

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 front-loaded sentence with the core behavior first and the use-case hint in parentheses; no wasted wording. It is perhaps too terse for what it leaves unsaid, but nothing present is superfluous.

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 one-parameter read tool with readOnlyHint and no output schema, the definition covers purpose and scope adequately. The main gap is return semantics: the plural 'facturas' and 'todos los periodos' suggest multiple possible matches, but the description never says whether it returns a list, a single invoice, or nothing.

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 one parameter with 0% schema description coverage, so the description must compensate. It does partially, clarifying that matching is on the exact number rather than a substring or partial search, but it adds no format or example detail for the 'numero' value.

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 states a specific verb and resource ('Busca facturas') plus a precise matching rule ('por número exacto') and scope ('en todos los periodos'). This implicitly distinguishes it from cs_get_invoice and cs_list_invoices, though no sibling is named explicitly.

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 parenthetical 'útil para no duplicar' gives one concrete use case (checking for an existing invoice before creating one), which is genuine when-to-use guidance. However, it never names alternatives such as cs_get_invoice or cs_list_invoices, nor states when not to use it.

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