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

Annotations already declare readOnlyHint, openWorldHint=false, idempotentHint and destructiveHint=false, so the safety profile is covered. The description still adds substantive, non-redundant behavior: it explicitly does NOT verify line existence, and it states concrete limits (64 KB input, 1 s per call, 1 MB result). The 'sin red, sin estado guardado' and 'determinista' lines largely restate 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?

Good front-loading (what it does first) and useful labeled sections (Cuándo / No para / Efectos / Límites). But the definition is long, duplicates the full text in both Spanish and English, and spends a whole clause on an irrelevant fiscal-rule scenario that should have been cut.

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-value explanation is not required, and the single parameter is simple and documented. The missing piece is trustworthy routing: nothing tells an agent when to pick this over phone-e164-validate or phone-parse, and the mis-scoped 'Cuándo' clause degrades an otherwise complete definition.

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?

One required parameter with 100% schema description coverage, so the schema baseline applies. The description contributes the accepted syntax families (3XX, 60X with region, 01 8000) and the E.164 output format, which help interpret the input, but it gives no examples or normalization behavior beyond the schema's own 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 and resource ('Verifica la SINTAXIS de un teléfono colombiano') and enumerates the accepted families (celular 3XX, fijo 60X con región, 01 8000) plus the E.164 output. The boundary 'No verifica que la línea exista' is a genuinely useful disambiguation. However, the sibling it names in 'No para' (co-plate-validate) is unrelated to phone validation, while the far more confusable siblings phone-e164-validate and phone-parse go unmentioned, so differentiation is misdirected.

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?

The 'Cuándo' clause is plainly wrong for this tool: it tells the agent to use phone validation when a Colombian tax/fiscal rule (DIAN, Ley Emiliani, COP, IVA, GMF, UVT) must be applied exactly — copy-paste residue from a fiscal tool. That actively steers an agent toward the wrong use case. The 'No para' exclusion of co-plate-validate is real guidance, which keeps this above a 1, but the primary when-to-use signal is misleading.

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