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

Annotations already cover the safe-read profile (readOnly, idempotent, closed-world), so the bar is low, but the description still adds real behavioral context: missing components are explicitly flagged as a lower limit or not computed and never estimated, and it discloses that ITBI comes from municipal law (41 cities) while notary/registration uses a 2026 table (21 states). The only gap is no indication of the shape of the returned breakdown.

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?

Two sentences, front-loaded with the country marker and the computed outputs, with no filler. The dense parentheticals (41 cities, 21 states, 55 cities) are informative but slightly clutter the read.

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 three-parameter calculator with no output schema, the description should ideally indicate what the response contains (amounts per component, totals). It covers coverage, method, and missing-data handling well, but leaves the return structure for the agent to discover.

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% and all three parameters are self-documented, so baseline is 3. The description adds contextual meaning by explaining that the applicable rate depends on the city (municipal law) and the state (notary table), but it says nothing about reference_value or how it interacts with price beyond what the schema already states.

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 ("Computes") and three named outputs (ITBI transfer tax, notary deed, registration) for a defined scope: a home purchase in one of 55 Brazilian cities. The leading "BRAZIL" tag and the country-specific cost components make it trivially distinguishable from the purchase_costs_be/de/es/it siblings.

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?

Usage is implied rather than stated: the description scopes it to "a home purchase in one of the 55 cities covered", which tells the agent when the tool applies and where coverage ends. It never names an alternative for adjacent questions (mortgage_payment_br, capital_gains_tax_br, guide_br) or says what to do when the city is outside coverage.

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