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

Annotations already declare readOnly, idempotent, non-destructive and closed-world, so safety is covered. The description still adds real value by stating determinism and concrete operational limits (64 KB input, 1 s per call, 1 MB result), which annotations do not carry. It does not explain the output shape, but 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 content (purpose, when, not-for, side effects, limits) is front-loaded in the Spanish section, with labels that scan well. The main cost is that the same content is largely repeated in English, and the English block also duplicates the inputSchema description, adding length without new information.

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 deterministic, read-only formatting tool with full parameter documentation and an output schema, the description covers everything an agent needs: what it produces, when to prefer it, what it is not for, side effects and hard limits. Nothing material 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 description coverage is 100%, so the baseline is 3. The description goes slightly beyond the schema by tying apocope to its linguistic effect (primer/tercer before a masculine noun) and showing the abbreviation forms (1.º, 1.ª), which helps the agent interpret the options rather than just their names.

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 with scope: "Escribe ordinales en español del 1 al 999 (primero, vigésimo tercero…)", including the gender, apocope and abbreviation variants. It also explicitly separates itself from the sibling that handles cardinal numbers, so an agent can distinguish the two without opening a 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?

Gives an explicit "Cuándo" trigger (Spanish text, numbers or dates must follow written language rules rather than approximation) and an explicit "No para" exclusion naming es-number-to-words as the alternative for large integers. Both the positive and negative routing conditions are stated.

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