Calculate mortgage PITI

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

Beyond the annotations, the description discloses that the tool is local-only and makes no network call, and that PMI is applied automatically when LTV > 80% and pmi_rate is provided. This adds meaningful behavioral context without contradicting the readOnlyHint or idempotentHint 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?

The description is three focused sentences with no filler. It front-loads the purpose, then efficiently explains the key parameter combinations and defaults that an agent needs to invoke the tool correctly.

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 appropriately explains both the return value (full PITI breakdown plus total interest) and the important input constraints. Minor details like the loan term default and exact handling when both down payment options are supplied are left to the schema and defaults, but overall the description is sufficient for reliable invocation.

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 coverage is only 40%, but the description compensates by explaining key relationships: down_payment and down_payment_percent are alternatives with a 20% default, property tax can be expressed annually or as a rate, and PMI behavior depends on LTV and pmi_rate. It does not describe every parameter, but the most decision-relevant semantics are covered.

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 'mortgage payment calculator' that returns a full PITI breakdown and total interest. It is clearly differentiated from sibling tools like compass_calculate_affordability and search tools by its local-only, calculation-focused purpose.

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 gives a clear context for when to use the tool: when a PITI breakdown and total interest are needed. It also provides concrete input-selection guidance (either down_payment or down_payment_percent, property tax alternatives, automatic PMI). It does not explicitly name alternatives or exclusions, but the intended use is clear.

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