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 'sin efectos secundarios / solo lectura / sin red' and 'determinista' sentences largely restate them. What is genuinely additive are the operational limits (64 KB JSON input, 1 s per call, 1 MB result), which the annotations do not convey.

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 logically ordered (what → when → not-for → side effects → limits), but the same material is presented in full Spanish and then again in English, and the schema's description field repeats the English block verbatim. That bilingual duplication costs space without adding information for the caller.

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?

An output schema exists, so return values need not be explained, and the description covers the remaining gaps an agent would care about: determinism, no network, size/time limits, and the sibling boundary. Only the handling of already-formatted NITs with embedded DV is left to the 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 both parameters (nit, dv) are documented in the schema, so the baseline is 3. The description clarifies that the DV is validated when supplied and shows the expected formatted output, but it adds no format or edge-case detail for `dv` or for NITs supplied with dots/dashes beyond what the schema already states.

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 precise verb+resource (computes the DIAN verification digit of a Colombian NIT), names the algorithm (mod 11 published by DIAN), and covers the validation/formatting facets plus an output example. It also explicitly separates itself from the sibling that could be confused with it (co-cedula-format).

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?

Gives an explicit 'Cuándo' with a concrete trigger (checking/formatting a NIT with its DV, e.g. before issuing an invoice) and an explicit 'No para' naming the alternative tool (co-cedula-format) for cédula syntax checks. 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.