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

Annotations already cover readOnly, idempotent, non-destructive and closed-world, yet the description adds genuinely new facts: no network access, no stored state, determinism, and concrete limits (64 KB input, 1 s per call, 1 MB result). It restates the read-only/no-side-effects point that annotations already make, which keeps it just short of a 5.

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 content is front-loaded and segmented into labelled blocks (Cuándo, No para, Efectos, Límites), making it easy to scan. The cost is that the entire text is duplicated in Spanish and English, roughly doubling length for no additional information.

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 single-parameter, read-only validator with an output schema present, the description supplies the deciding details: input semantics, sibling disambiguation, determinism, and execution limits. Nothing an agent needs to call it 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 documented there, so the baseline would be 3. The description still adds real meaning beyond the schema by specifying the 15-digit length and the Luhn check-digit requirement, which the schema's 'up to 64 chars' wording 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?

The description pairs a specific verb ('Valida') with a specific resource ('IMEI de 15 dígitos') and states the output decomposition into TAC and serial number. It also explicitly distinguishes itself from luhn-validate, so an agent can tell the two apart 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?

It gives an explicit 'Cuándo' condition (offline verification of format and check digit before use) and an explicit 'No para' exclusion naming the sibling tool luhn-validate. This is the when/when-not/alternatives pattern done fully.

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