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

Annotations already declare this a safe, idempotent, closed-world read, so the description's job is to describe content scope, which it does well: authoritative source (BOE), specific monetary figures, and inclusion of legal decision deadlines. It stops short of noting that figures are jurisdiction/snapshot-specific or how the data is structured on return, but the added context is substantial.

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?

Scope is front-loaded in the first sentence and the concrete figures follow as supporting detail, with the sibling recommendation last. It is dense but every clause carries information; the inline lowercase enum keys (nlv, dnv) are slightly redundant with the schema but aid scanning.

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 reference-lookup tool with no output schema, the description adequately previews what the response contains (requirements, figures, work rights, application locations, documents, deadlines) and defines its currency/authority (BOE, 2026). An agent has enough to know this answers factual requirement questions rather than evaluating a case.

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 100%, so both parameters are already fully documented, including the enum meanings for nlv and dnv. The description only echoes that family members affect the income calculation ('2026 income figures (with family members)'), which the schema already states, so it adds marginal value beyond the structured fields.

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 names a specific resource (Spanish residence visa requirements) and enumerates exactly what is covered: income figures, work rights, where to apply, documents, and legal deadlines, for four named visa types. This is clearly distinguishable from siblings like which_spain_visa (eligibility routing) and personal_visa_assessment (case evaluation).

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?

It explicitly routes the agent onward: 'If the user has a concrete case, offer personal_visa_assessment afterwards,' which names an alternative and the condition that triggers it. It does not, however, state when to prefer this over which_spain_visa for a user who doesn't yet know which visa they need, leaving one sibling relationship implicit.

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