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

Annotations already declare readOnly, idempotent, non-destructive and closed-world, but the description adds genuinely new context: determinism, concrete limits (64 KB JSON input, 1 s per call, 1 MB result) and no stored state. These operational bounds are not derivable from the annotations and directly affect how an agent should size its input.

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 the core action, then labeled sections (When / Not for / Side effects / Deterministic / Limits) that are easy to scan. The Spanish and English versions duplicate the same content, which roughly doubles length without adding information, costing a point.

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, annotations cover the safety profile, and all three parameters are documented in the schema. The description fills the remaining gaps (limits, determinism, sibling routing), leaving nothing an agent needs in order to 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 text, start and separator are already fully documented with defaults and bounds. The description only restates that numbering starts at a given number with a chosen separator, adding no syntax or format detail beyond the schema. Baseline 3 applies.

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 ('Numera cada línea, alineando a la derecha' / 'Prefixes each line with its line number, right-aligned') and adds the start-number and separator scope. It explicitly names the sibling it is not (lines-sort), so an agent can distinguish it without opening the 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?

Provides an explicit 'Cuándo'/'When' condition (exact transformation, comparison or measurement of text) and an explicit 'No para'/'Not for' exclusion pointing to lines-sort for locale-aware sorting. 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.