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

Annotations already declare readOnly/idempotent/non-destructive/closed-world, so the safety restatement ('solo lectura, sin red, sin estado guardado') adds little. It does add value beyond structured data with hard limits (64 KB JSON input, 1 s per call, 1 MB result) and an explicit determinism guarantee.

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 purpose is front-loaded and the ES/EN split is parallel, but the entire description is duplicated in Spanish and English, so roughly half the text is redundant for any given reader. The 64 KB/1 s/1 MB limits are useful but phrased in a boilerplate block.

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?

With an output schema present, return values need not be explained; purpose, exclusions, side effects, determinism and limits are all covered. Minor gap: how negative signs are rendered in words is not stated, though the schema pattern allows them.

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 baseline is 3, but the description adds meaning: it states the accepted magnitude range (|n| < 10^18) and shows what the ordinal flag actually produces ('one hundred twenty-third' vs 'one hundred twenty-three'). That is real semantic value beyond the boolean's schema text.

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?

Specific verb+resource: 'Spells an integer (|n| < 10^18) in English words, as a cardinal ... or ordinal', with concrete output examples. It is immediately distinguishable from the near sibling es-number-to-words, which it names.

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?

Explicitly names the alternative and the exclusion: 'Not for: spelling an integer up to 10^18 in Spanish words (es-number-to-words)'. The 'When' clause ('a numeric result has to be exact or reproducible instead of estimated') is a bit vague since word-spelling is always deterministic, but the routing signal against the sibling is clear.

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