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

Annotations already cover read-only, closed-world, idempotent and non-destructive, so the description's job is to add more — and it does: no network access, no stored state, deterministic output, plus concrete limits (64 KB input, 1 s per call, 1 MB result). The determinism and latency/size ceilings are operationally useful details absent from the annotations.

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 core purpose and organized under labeled sections (Cuándo / No para / Efectos / Límites), so scanning is easy. The full Spanish and English duplication roughly doubles length for no added information, which keeps it short of a 5.

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?

A single-parameter, read-only validation tool with an output schema: the description covers scope, exclusions, determinism and resource limits, and the output schema carries the return shape. 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%, so the baseline is 3, but the description adds real meaning the schema lacks: the value must be a 9-digit routing number validated with a 3-7-1 checksum, whereas the schema only says 'string up to 20 chars'. The only small gap is not explaining why maxLength is 20 when 9 digits are expected.

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 un número de ruta ABA de EE. UU.') plus the algorithm (9 dígitos, checksum 3-7-1) and the extra output (distrito de la Reserva Federal). It also explicitly names the sibling it is not, iban-validate, so an agent can separate it from the other identifier validators without opening a 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?

The 'Cuándo' clause gives the triggering condition (verify format and check digit offline before using an identifier) and the 'No para' clause names the excluded case and the alternative tool (iban-validate). Both when-to-use and when-not-to-use are explicit.

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