Calculate mortgage payment (local)

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

Annotations already declare readOnlyHint and idempotentHint, and the description goes further by saying 'No network call — fully deterministic,' explaining PMI auto-application at LTV > 80%, the 20% down payment default, and property tax input alternatives. No contradiction with annotations.

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?

Four sentences, front-loaded with scope and output, no filler. Every sentence contributes a distinct piece of information: local behavior, return value, input alternatives, and PMI 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?

For a 10-parameter tool with no output schema, the description covers the return contents, defaults, parameter selection rules, and conditional PMI behavior. An agent has enough information to select and invoke the tool correctly using the schema plus this description.

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 only 40%, but the description compensates for the key ambiguities: 'either down_payment OR down_payment_percent; defaults to 20%', property tax as annual amount or rate, and the pmi_rate condition. It does not document every parameter, but the omitted ones are either self-explanatory or covered by schema descriptions.

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 verb and resource: a 'Local-only mortgage payment calculator' that 'Returns a full PITI breakdown' plus total interest. This clearly separates it from data-fetching siblings like redfin_search_properties or redfin_calculate_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?

The description explicitly frames when to use it: 'safe to use for scenario comparison without burning a fetch' and labels it as local-only. It does not name sibling alternatives or state when NOT to use it, so there is minor room for improvement.

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