Project cumulative buy-vs-rent cost over N years

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

The description explains internal behavior: 'Accounts for down payment, closing costs, monthly PITI, maintenance (~1%/yr default), appreciation (~3%/yr default), rent growth (~3%/yr default), and the opportunity cost of the down payment (renter invests it at investment_return_rate, default 6%/yr).' It states 'Returns year-by-year cumulative costs, break-even year, and the net difference at horizon' and 'No network — pure local math.' These detail effects beyond annotations (readOnlyHint, idempotentHint) and do not contradict them.

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 concise and well-structured: two paragraphs—first explaining the tool's function and inputs, second providing a critical note about data sourcing. It front-loads the primary purpose and uses clear language. Every sentence adds value, with no repetition of schema fields.

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?

Given 15 parameters and no output schema, the description is fairly complete: it explains the model, outputs (year-by-year costs, break-even, net difference), and the need for a rent estimate. It could mention the relationship to siblings (e.g., similar to homes_calculate_mortgage but adds rent comparison) and clarify the absence of network dependency (already stated). Still, it covers the essential context for effective tool selection.

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?

With 0% schema description coverage, the description must compensate. It does so by explaining many parameters in context: down payment, closing costs, monthly PITI, maintenance (maintenance_rate), appreciation (appreciation_rate), rent growth (rent_growth_rate), opportunity cost (investment_return_rate). However, not every parameter (e.g., hoa_monthly, insurance_annual) is explicitly named, though they are implied by 'closing costs' and 'PITI'. Overall, it adds substantial meaning 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?

The description clearly states the tool's purpose: 'Project the cumulative cost of buying a home versus renting a comparable place over N years.' It specifies the factors considered (down payment, closing costs, PITI, maintenance, appreciation, rent growth, opportunity cost) and distinguishes from siblings like homes_calculate_mortgage by focusing on the buy-vs-rent comparison. The mention of same math contract as zillow_estimate_rent_vs_buy further aids differentiation.

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 description provides explicit usage guidance: 'NOTE: caller must supply `monthly_rent` — homes.com does not publish rental estimates...' and suggests alternative tools (zillow_get_property, redfin_get_comparable_rentals) for obtaining a rent estimate. It also indicates when not to use (if no rent estimate available) and contextualizes that this is pure local math with no network dependency.

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