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

Annotations already declare a safe, idempotent read, so the bar is lower; the description still adds real behaviour: Belgium has no legal debt-to-income rule, the 33% share and 3.5% rate are example assumptions the caller may change, and results depend on regional purchase costs. It does not say whether unsupported municipalities raise or silently default.

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?

Front-loaded with the country scope and the core computation in the first sentence, with the modelling caveat second. The trailing URL/alternate-language references are padding for an agent but do establish provenance, so not a full 5.

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?

No output schema exists, yet the description says what is returned (achievable capital and highest home price) and anchors it to a real-world calculator. Combined with 100% parameter coverage and safe read annotations, an agent has everything needed to call and interpret it.

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 schema already documents all nine parameters with defaults and ranges, making 3 the correct baseline. The description reinforces that share_of_income_pct and interest_rate_pct are adjustable example defaults and links region to purchase costs, but adds no format or constraint detail beyond the schema.

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 computation (capital a fixed-rate loan allows, plus the maximum home price net of regional purchase costs) from a single named input, which clearly separates it from cost tools like purchase_costs_be or price tools like house_prices_be. It stops short of explicitly naming a sibling to route the agent to.

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 by the income-in / capacity-out framing, but there is no explicit 'use this when...' or 'use X instead when...' guidance against the many neighbouring tools (purchase_costs_be, compare_regions_be, house_prices_be). The caveat about assumptions is context, not routing.

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