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

Annotations already declare readOnly, idempotent, closed-world and non-destructive, so the safety profile is free; the description adds real value on top with hard limits (64 KB input, 1 s per call, 1 MB output) and a determinism guarantee. The 'sin efectos secundarios / sin red / sin estado' sentence largely restates the annotations rather than extending them, which keeps this from a 5.

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 text is dense and front-loads the feature list, but the description then repeats itself as a parallel EN block that adds no new information and even self-references '[EN completo / full EN: inputSchema.description]'. That meta-pointer and the duplication consume space without earning it.

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 4-parameter tool with a nested object input and an existing output schema, the description supplies everything an agent still needs: supported template syntax, explicit exclusions, when/when-not, side-effect profile, size and time limits, and determinism. Return shape can be safely omitted because an output schema exists.

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; the description does clarify escaping semantics ({{var}} escaped vs {{{raw}}}/{{&raw}} unescaped), which gives meaning to escape_html. However, the 'strict' switch — the parameter most likely to cause unexpected failures — is never mentioned in the description, and data/template typing is left entirely to the schema.

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 (render a Mustache template) and immediately bounds the feature subset: variables with HTML escaping, raw braces, dotted names, sections, list loops, inverted sections, comments, and explicit exclusions (no partials, lambdas or code). It also names the sibling template-render is not (prompt-template-fill), so an agent can disambiguate without opening either 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?

Explicit 'Cuándo' list enumerates concrete scenarios (URLs, HTTP headers, tokens, versions, IP ranges, HTML/Markdown, agent files) and an explicit 'No para' that routes placeholder filling to prompt-template-fill. Both the inclusion and exclusion conditions are stated, which is the top of the scale.

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