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

Annotations already declare readOnlyHint, idempotentHint, openWorldHint=false and destructiveHint=false, so the safety profile is covered; the description still adds determinism and concrete limits (64 KB input, 1 s per call, 1 MB result). Minor deduction because the tail line ('[EN completo / full EN: inputSchema.description]') is meta-text rather than disclosure, and the limits duplicate the schema description.

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?

Front-loaded with purpose followed by When/Not-for/effects/limits, which is good structure, but the Spanish and English blocks are near-verbatim duplicates and the trailing pointer to inputSchema.description is wasted text. Efficient content, roughly double the length it needs to be.

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?

Output schema exists, so return shape need not be described; the description still covers accepted format, determinism, side-effect posture and resource limits. Nothing an agent needs to invoke this correctly 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?

Schema coverage is 100% and the single parameter is already documented, so baseline is 3; the description earns a point by enumerating the accepted cron syntax (5 fields, lists, ranges, steps, names, @daily macros) that the schema's one-line 'Cron expression' field does not convey.

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?

States a specific verb and resource ('Valida una expresión cron de 5 campos y la describe en inglés y español, con los valores expandidos') plus the accepted grammar (lists, ranges, steps, names, macros). It also explicitly names the sibling it is not (cron-next-runs), so an agent can separate the two without opening either schema.

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?

Explicit 'Cuándo:' clause scopes it to exactness-critical date/timezone/calendar results, and an explicit 'No para:' clause routes the next-N-runs case to cron-next-runs. Both the when and the when-not are stated, not inferred.

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