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

Annotations already declare readOnlyHint=true and openWorldHint=false, so the safety profile is covered. The description usefully adds behavioral detail beyond that: the 65% LTV revolving cap, 80% total secured borrowing limit with an A lender, OSFI stress-test TDS qualification, and coverage of B/Private tiers. It stops short of describing edge cases or default fallbacks.

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 tight sentences, front-loaded with the comparison purpose followed by a compact enumeration of the computed outputs. Every clause carries information; no filler.

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 14 parameters and no output schema, the description carries the return-value burden and does so well by naming the outputs (borrowing capacity, monthly payments, TDS qualification, tier equivalents). It is nearly complete, though it omits the optional default behaviors (e.g., prime rate, tier rate defaults) that the schema documents.

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 71%, so the schema already documents most inputs. The description adds domain meaning that maps to parameters (65% LTV tie to homeValue/outstandingFirstMortgage, A/B/Private lending to secondMortgageLenderTier, OSFI rate), but does not explain individual parameters beyond the schema baseline.

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 (compare) and two named resources (HELOC vs second mortgage) for a distinct jurisdiction (Canada), which clearly separates it from siblings like mortgage_payment or mortgage_affordability. An agent can tell what it does without opening the schema.

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 'Compare a HELOC against a second mortgage for tapping home equity,' but there is no explicit when-to-use, when-not-to-use, or routing to sibling tools (e.g., 'for a plain affordability check use mortgage_affordability'). The agent must infer the context.

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