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

Annotations already declare readOnly, idempotent and non-destructive, but the description adds real value beyond them: no network access, no stored state, determinism guarantees, and concrete operational bounds (64 KB input, 1 s per call, 1 MB result). Those limits are the kind of information an agent cannot infer 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?

The Spanish/English duplication roughly doubles the length, but the content is front-loaded and cleanly labelled (When / Not for / Side effects / Deterministic / Limits), so every clause still carries information. Removing the redundancy would improve density without losing meaning.

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 two-parameter pure function with an output schema, nothing needed is missing: semantics, exclusions, side effects, determinism and size/time limits are all present. An agent can decide to call it and predict its behavior from the description alone.

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 two parameters are already documented, but the description adds genuine semantics by explaining what the patch value actually does (recursive merge, null deletion, replacement) rather than just saying 'any JSON value'. It stops short of per-parameter guidance, so it does not fully supersede the schema baseline.

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 names a specific verb and resource ('Aplica un JSON Merge Patch (RFC 7386)') and immediately defines the operation's semantics: objects merge, null deletes, other values replace. That semantic summary alone distinguishes it from json-merge-patch-create, which is explicitly named as out of scope.

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 provides an explicit 'Cuándo' block and a 'No para' exclusion that names the sibling json-merge-patch-create. The positive 'when' clause, however, is broad boilerplate ('transformar, comparar o revisar con exactitud datos estructurados') that would apply to many sibling tools, so the exclusion does more discriminating work than the inclusion.

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