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

Annotations already declare readOnly, non-destructive and closed-world, so the safety profile is covered. The description adds two genuinely non-annotation facts – the data is public and no key/credential is required ('Datos públicos. Sin clave.') – but says nothing about response shape, coverage, or failure modes when the code is unknown.

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?

Three short, front-loaded Spanish sentences with no filler; the core purpose leads and the optional-parameter note follows. Nothing is redundant, though it is arguably terse enough to leave gaps.

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 2-parameter, read-only lookup with no output schema and adequate annotations, the description is close to sufficient. It would be stronger if it summarized what the módulos response contains (indexes, limits, activity assignment) so the agent knows what to expect.

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 0%, so the description carries the load. It explains the 'slug' parameter's purpose (disambiguating codes with multiple activities) but offers nothing on 'code' beyond it being an IAE identifier, and does not surface the string pattern constraints in the schema.

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 specific verb/domain: it returns the 'Régimen de estimación objetiva (módulos)' for an IAE code, which is a concrete resource that an agent can distinguish from generic IAE lookups. It stops short of explicitly contrasting itself with nearby siblings like detalle_iae, so it earns a 4 rather than a 5.

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?

Usage is only implied: the tool is for looking up módulos data for a given IAE/activity code. The description does give a conditional hint for the slug ('para desambiguar códigos con varias actividades'), but never states when to prefer this tool over buscar_codigo or detalle_iae.

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