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

Annotations already establish the safe-read profile (readOnlyHint, idempotentHint, destructiveHint=false), so the bar is lower. The description adds genuine value by disclosing the return payload fields — year, provisional flag, and source (Ministerio de Hacienda) — plus the flatin.es page reference, which matters because no output schema exists. It stops short of noting rate-limit or coverage caveats.

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?

A single compact sentence with the resource definition front-loaded and the returned fields trailing. No filler sentences, though the trailing clause is a slightly dense list.

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 simple two-parameter lookup with no output schema, the description covers what the value means, what accompanies it (year, provisional flag, source), and points to the originating page. Combined with annotations covering the safety profile and a 100%-covered schema, the definition is essentially complete; only cross-tool routing guidance is absent.

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 both parameters (municipio with its four accepted forms, and the locale enum defaulting to en) are already fully documented in the schema. The description adds nothing beyond that, which is the expected baseline here.

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+resource+scope: the yearly IBI urbana rate for a Spanish municipality, expressed as % of cadastral value. This is unambiguous and highly specific. It does not differentiate itself from siblings like purchase_costs or non_resident_tax, so it falls short of 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?

No statement of when to use this tool versus alternatives such as purchase_costs or non_resident_tax, and no preconditions or exclusions. Usage must be inferred purely from the tool name and the property-tax definition.

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