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

Annotations already establish read-only, idempotent, closed-world behavior, so the description only needs to add output semantics – and it does, disclosing that results are returned for 3%, 5%, 10% and 20% down side by side plus a PMI applicability flag. That comparison behavior is not derivable from the three scalar input parameters and is genuinely useful with no output schema present.

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?

A single front-loaded sentence that names every output, the comparison tiers, and the PMI condition, followed by a reference URL. No filler sentences and nothing to trim.

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 return-value burden and mostly succeeds: it enumerates the computed figures and the PMI flag. It could still be clearer on the response shape of the side-by-side comparison and how currency affects formatting, but an agent has enough to call it 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%, with each of price, downPct, and currency documented including defaults and bounds, so the baseline is 3. The description adds only the framing that the price is a 'home price' and that down percentages matter at the 20% threshold, not any syntax 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 concrete outputs (down payment, loan amount, LTV, PMI flag) against a clear input (home price), which is more specific than a generic 'calculator'. It does not, however, name or distinguish itself from nearby siblings like loan_to_value_calculator or mortgage_calculator, so an agent must infer the boundary.

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 only implied by the scenario ('for any home price') and the 20%-equity PMI reference; there is no explicit when-to-use, when-not, or alternative tool named. Adequate to guess the intent but leaves the agent to decide between this and the LTV/mortgage siblings.

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