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

Annotations already declare readOnlyHint=true, non-destructive, and closed-world, so safety is covered. The description adds useful behavioral context: the exact rule tiers, that it also determines CMHC insurance applicability, and that it returns a premium rate. It does not discuss assumptions such as occupancy type or amortization, which keeps it from a 5.

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?

The description is a single front-loaded sentence that efficiently names the calculation, jurisdiction, rule set, and outputs. The parenthetical tier breakdown is dense but earns its place by clarifying an otherwise complex rule.

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 carries the burden of explaining what is returned, and it does so by naming the minimum down payment, CMHC insurance applicability, and premium rate. It is complete enough for a one-parameter calculator, though it omits assumptions that could affect results.

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 the sole parameter, homePrice, is documented in the schema. The description does not add syntax, constraints, or format meaning beyond what the schema already provides, so the baseline of 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?

The description states a specific calculation (minimum down payment) for a specific jurisdiction (Canadian home) under a specific rule set (Dec 2024 CMHC). It also names the outputs (CMHC insurance applicability and premium rate), which clearly distinguishes it from siblings like mortgage_payment or mortgage_affordability.

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 Canadian CMHC rule context, but the description does not explicitly say when to use this tool versus siblings such as mortgage_payment or mortgage_affordability. No exclusions or alternative-selection guidance are provided.

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