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

Annotations already cover read-only, idempotent, non-destructive, no-network; the description goes further by disclosing failure semantics on malformed sequences ('no adivinar' / 'Fails... instead of guessing'), determinism, and concrete limits (64 KB input, 1 s per call, 1 MB output). Those operational constraints are not derivable 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 purpose, then when/not-for, then side effects, then limits — a clean order with no filler sentences. The only inefficiency is the full ES/EN duplication, which roughly doubles length for an agent reading both halves.

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 no explanation; the description instead covers the things the schema cannot: error behavior, determinism, size/time limits, and the alternative tool. Nothing needed to invoke it safely 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 for the enum: in 'form' mode a literal '+' is treated as a space, which the schema only names as an enum value. The 'text' parameter itself needs no extra explanation given the schema's example.

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 ('Decodifica texto con codificación porcentual' / 'Decodes percent-encoded text') and immediately names the sibling it is not ('No para: codificar texto para URL (url-encode)'). An agent can distinguish it from url-encode, url-normalize, and url-parse without opening any 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 'When:' clause defining the conversion task and an explicit 'Not for:' clause routing to url-encode. This is the when/when-not/alternative triad the rubric reserves 5 for.

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