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

Annotations already carry readOnlyHint=true, so the safety profile is covered. The description adds a genuine behavioral trait beyond the annotation: for on-demand purchase requests the tool will honestly respond that the capability is unavailable rather than fabricate a result — useful anti-hallucination guidance. It is consistent with the read-only annotation, so no contradiction.

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 purpose is one short sentence and the note adds one more, which is appropriately compact for a two-parameter read tool. However, the note contains roadmap jargon ('Fase 2') that belongs in release notes rather than a tool definition, and its meaning is ambiguous — the sentence is confusing, not merely concise.

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?

This is a simple 2-parameter read-only tool with an output schema and a clear resource, so the description is close to sufficient. It is adequate but leaves unspecified what the returned annual accounts contain (e.g., balance sheet, income statement) and provides no context on data coverage; the odd note wastes a sentence that could have carried that information.

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 coverage is only 50% (ejercicio has a format example; empresa_id has no description), and the tool description does not compensate. It merely re-states that the tool involves a company and a fiscal year, which just echoes the parameter names, adding no format, source, or meaning for either parameter.

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?

The description clearly identifies the resource — annual accounts of a company for a fiscal year — which is distinct from all seven siblings (BORME acts, contracts, risk, subsidies, etc.), so an agent can select it correctly. It lacks an explicit verb (it is a noun phrase, not 'retrieves/gives'), and the appended roadmap note slightly muddies the core purpose sentence.

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?

No guidance is given on when to use this tool versus alternatives: no siblings are referenced and no conditions or exclusions are stated. The Phase 2 note hints at an unavailability for on-demand purchase but does nothing to help an agent choose between this and asientouno_informe_completo or asientouno_riesgo_empresa.

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