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

Annotations already declare readOnlyHint=true, idempotentHint=true, openWorldHint=false, so the safety profile is covered. The description adds genuinely useful behavior: every output line cites law, article, and verification date, and it discloses that fees use 'the general rate of the tax territory' and 'official scales' rather than any negotiated figure.

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 sentences, front-loaded with the purpose, with no filler. The legal-citation and disclaimer sentences are compact and additive, though the tax-component enumeration is somewhat dense for an opening clause.

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?

With no output schema, the description does useful work by signaling an itemized, law-cited result. Combined with a fully documented 5-parameter schema covering the mortgage carve-out (Ley 5/2019), an agent has enough to call it correctly; only the return structure and estimation assumptions remain slightly under-specified.

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 place, locale, new_build, price_eur, and mortgage_eur are all fully documented in the schema. The description's tax-regime explanation largely restates the new_build schema text, adding little parameter-level detail beyond confirming that place drives the applicable regional rate.

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 precise resource (taxes and fees of buying a home in Spain) and enumerates the specific components computed: VAT + AJD for new builds, ITP for resales, plus notary and registry fees. This cleanly separates it from siblings like ibi_rate (annual property tax) and non_resident_tax.

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?

The scope implies usage (compute closing costs for a purchase) and the new_build distinction routes between the two tax regimes. However, there is no explicit guidance on when to use this versus compare_places or newbuilds_in_place, and no stated prerequisites or exclusions beyond the 'estimate, not tax advice' caveat.

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