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

Annotations already declare readOnlyHint, idempotentHint, openWorldHint=false and destructiveHint=false. The description reinforces these but also adds operational detail annotations don't carry: no network, no stored state, deterministic output, and concrete limits (64 KB input, 1 s per call, 1 MB result). The duplication of annotation facts slightly dilutes the added value.

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?

Well front-loaded with labeled sections (Cuándo / No para / Efectos / Límites) that make scanning easy. However the full Spanish text is then repeated verbatim in English, and the schema description repeats the EN block again, so the total surface is roughly double what is strictly needed.

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?

Given an output schema exists and annotations cover the safety profile, the definition supplies everything else an agent needs: precise validation semantics, exclusions, side-effect posture, determinism, and size/time limits. Nothing material is left to inference.

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 param is exemplified, so the baseline is 3. The description adds real semantic meaning by explaining what the component segments of the input represent and clarifying the tool never fills in a missing check digit, which helps an agent interpret the expected input shape.

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+resource with exact scope: validates an 18-digit Mexican CLABE, breaking down structure (bank 3, plaza 3, account 11, check digit 1) and the 3-7-1 mod-10 checksum. It also bounds the operation ('solo valida; no calcula dígitos faltantes'), so an agent knows precisely what is and isn't performed, distinguishing it from generic checksum tools.

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 (check a user-supplied account number offline before storing/using it) and an explicit 'No para' naming the sibling mx-curp-validate. Minor gap: the when-to-use text widens scope to 'LatAm o España' IDs, which is broader than CLABE and could mislead an agent into routing a Spanish IBAN here.

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