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

Annotations already declare readOnly, idempotent, non-destructive and closed-world, so the safety profile is covered. The description still adds value beyond them: deterministic output for identical input, no network access, no stored state, and concrete limits (64 KB input, 1 s per call, 1 MB result). It does not describe the shape of the returned match, though an output schema exists.

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 core sentences are front-loaded and efficient, but the definition is repeated three times (Spanish body, English body, and an identical inputSchema.description) plus a meta pointer '[EN completo / full EN: inputSchema.description]' that adds nothing. The generic artifact list in 'Cuando' is template filler that does not earn its place.

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, read-only parsing tool with an output schema, the description covers purpose, exclusion, determinism, resource limits and matching semantics. An agent has everything needed to select and call it correctly.

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 description coverage is 100%, so parameter types and bounds are already documented. The description nonetheless adds real semantics the schema lacks: that ordering follows q-value priority and that the matching against 'supported' is exact first, then by primary language — this tells the agent how the optional array actually affects the result.

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 opening sentence names a specific verb and resource: parses an Accept-Language header, sorts by q-value, and picks the best match from supported locales, with the exact-then-primary fallback rule spelled out. It also names the sibling it is not (http-headers-parse). The value is slightly diluted by the boilerplate 'Cuando' list of unrelated artifacts (URL, IP range, HTML document) that applies to the whole suite rather than this tool.

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?

There is an explicit 'No para' clause naming http-headers-parse as the alternative for raw header blocks, which is real routing guidance. The positive 'Cuando' clause, however, is generic suite-wide boilerplate rather than conditions specific to this tool, so the agent gets one sharp exclusion but a fuzzy inclusion criterion.

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