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

Annotations already cover the safety profile (readOnly, idempotent, non-destructive, closed-world), so the bar is low. The description nevertheless adds real domain behavior: the 2% / 1.1% basis on cadastral value and the 24% / 19% applied rate, plus the tax year, which an agent can use to sanity-check or explain the result.

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 dense sentence with the country and the tax name front-loaded, and no filler. The nested parentheticals carry rate detail that is genuinely useful, though the stacking makes it slightly heavy to parse.

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 the heavy lifting by disclosing the full calculation basis and the year, which is what an agent needs to call it correctly. It stops short of saying what comes back (a euro amount) or confirming that share and days-owned prorate the result.

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 the baseline is 3. The description restates the rate logic that the schema fields (values_revised -> 1.1%, eu_eea_resident -> 19%) already document, adding reinforcement rather than new parameter meaning; share_pct and days_owned go unmentioned.

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 and resource: computing Spanish non-resident income tax (IRNR) on imputed income of a non-let home for 2026. The scenario described ('a home a non-resident keeps without letting it') is unmistakably distinct from siblings like purchase_costs_es, mortgage_payment_es or property_tax_us.

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 description pins down the scenario well enough to imply when the tool applies (non-resident, property not rented out). However, it never states an exclusion or names an alternative for a related case such as a rented-out property, leaving the agent to infer boundaries.

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