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

Annotations already declare readOnlyHint, idempotentHint, openWorldHint=false and destructiveHint=false, so safety is covered; the description nevertheless adds unique operational constraints: no network access, no stored state, and concrete limits (64 KB input, 1 s per call, 1 MB result). The determinism sentence largely restates idempotentHint, which keeps it out of the top score.

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 the verb and what is validated, then labeled sections (Cuándo / No para / Efectos / Límites) that are easy to scan. It loses a point for the full ES/EN duplication, which repeats the same content twice inside one description (and a third time in inputSchema.description).

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 validator with an output schema, everything the agent needs is present: what is validated, the non-North-American check-digit caveat, the alternative tool, side effects, and size/time limits. Return value details are correctly left to the output schema.

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 there is a single parameter, so baseline would be 3; the description earns more because it clarifies the actual contract where the schema is loose — the schema allows up to 20 chars, while the description states the VIN must be 17 characters and excludes I/O/Q. That resolves a real ambiguity the schema alone leaves open.

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 (valida) and resource (VIN de 17 caracteres) and enumerates exactly what is checked/decoded: allowed characters, check digit at position 9, WMI, model year, region. It also names the sibling it is not (imei-validate), so an agent can separate it from the many other *-validate tools without opening schemas.

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 (verify format and check digit offline before use) and an explicit 'No para' clause routing the agent to imei-validate for 15-digit IMEIs. Both the use case and the exclusion 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.