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

Annotations already declare readOnlyHint, idempotentHint and destructiveHint=false, so the 'Read-only' line largely repeats structured data. However, it adds two useful facts not in annotations: 'Rates are examples' (data reliability disclaimer) and the return contents (payment, cash-to-close, total interest), which matters since no output schema exists.

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?

Three short sentences, front-loaded with the operation and scope, then outputs, then the read-only/rates disclaimer. 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 no output schema, the description usefully names the three returned values, which is more than most. But for a 9-parameter nested tool with 0% schema coverage it leaves multiple input parameters unexplained and gives no guidance on rate/cost assumptions.

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 0% across 9 top-level params and nested scenario fields, so the description must carry the load. It mentions loan type, rate, down payment, term and discount points, but omits creditScore, hoaMonthly, insuranceMonthly, propertyTaxRatePercent, monthlyTaxOverride, vaFirstUse/vaDisabilityExempt, and never clarifies downPaymentUnit or the points semantics.

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 resource (2-4 loan scenarios) and enumerates the dimensions compared (type, rate, down payment, term, points) on a single purchase price. It does not distinguish itself from calculate_mortgage_payment or calculate_buydown, so it stops short of 5.

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 'compare 2 to 4 scenarios' framing implies this is the multi-scenario tool versus the single-payment siblings, but it never says when to pick it over calculate_mortgage_payment or when not to use it. Usage is implied rather than stated.

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