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

Annotations already declare readOnlyHint, idempotentHint and openWorldHint=false; the description reinforces this and adds genuinely new operational facts the annotations cannot carry: determinism, 64 KB input cap, 1 s per-call budget, 1 MB output cap, and no network/stored state. That is substantial value beyond structured fields.

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 differentiator, which is good, but the body is inflated by full Spanish/English duplication and a stray artifact ('[EN completo / full EN: inputSchema.description]') that costs tokens without informing. The duplicated text also creates the URL-slug contradiction, so length is doing harm rather than adding precision.

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 read-only, single-purpose transformer with a full output schema, the description covers usage, exclusions, side effects, determinism and limits — nearly everything an agent needs. The remaining gap is the 'URL slug' vs 'not for URLs' inconsistency, which could cause a caller to pick the wrong tool.

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 schema already documents enye enum values, defaults, text maxLength 4096 and max_length bounds. The description adds only marginal semantics (the ñ-mapping intent and stopword examples), and never mentions the max_length parameter or the interaction between max_length and ñ expansion.

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?

Names a concrete verb+resource (build a slug) and a distinguishing specialty (ñ preserved/transliterated as ni/ny/nn/keep) that separates it from generic slugging tools. However, the English text says it 'Builds a URL slug' and then immediately says it is 'Not for: making a URL slug (text-slug)', which muddies the core purpose for an English-reading agent.

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?

Explicit 'When' clause plus a 'Not for' clause that names the alternative sibling (text-slug), which is exactly the routing information an agent needs. The 'When' condition ('Spanish text, numbers or dates… by the written rules of Spanish') is broader and vaguer than the actual slugging capability, so selection is only mostly unambiguous.

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