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

Annotations already declare readOnly, idempotent, non-destructive, and closed-world, so the safety profile is covered without the description. The description adds that outputs are "estimates" and include PMI/property tax breakdowns, which is useful behavioral context, but it omits conditions such as when PMI is applied or how estimates are derived.

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-loads the purpose, then output shape, then a cross-reference — a sensible ordering with no filler. The inline return-field listing is somewhat redundant given an output schema exists, costing a little density but not enough to break the structure.

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 annotations covering safety, full schema coverage on all 4 params, and an output schema present, most structured burden is elsewhere. The remaining gap is sibling differentiation — the description never states how this differs from calculate_mortgage or calculate_mortgage_insurance, which is the main thing an agent needs to route correctly.

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% — every parameter (years, home_price, annual_rate, down_payment_pct) has its own description and defaults/ranges. The description adds no syntax or semantic detail beyond the schema, so the baseline 3 applies.

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 ("Calculate US mortgage") and specifies the distinguishing scope: PMI, property tax, and insurance estimates that a plain mortgage calc would not include. It does not, however, explicitly distinguish itself from the close sibling calculate_mortgage, so the agent must infer the US-specific scope from the name alone.

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 only routing hint is "See list_bundles for related 'finance-us' calculators," which points at a discovery tool rather than naming a competing alternative. There is no when-to-use/when-not guidance against calculate_mortgage or calculate_mortgage_insurance. The US prefix implies usage context but no explicit selection criteria are given.

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