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US Mortgage Calculator

by com.usmortgagecalc

Build an amortization schedule

calculate_amortization
Read-onlyIdempotent

Payment-by-payment breakdown of how a loan is repaid, showing the split between principal and interest and the falling balance. Use granularity 'monthly' for the first years in detail, 'yearly' for a whole-term overview. Also reports how much sooner extra principal pays the loan off.

Input Schema

TableJSON Schema
NameRequiredDescriptionDefault
stateNoFull US state name, for example "Texas". Used to look up the average property tax rate. Either this or propertyTaxRatePercent is required.
loanTypeNoLoan programme. Affects mortgage insurance and upfront fees.conventional
homePriceYesPurchase price of the home in US dollars.
monthlyHoaNoMonthly homeowners association dues in US dollars.
granularityNoYearly returns one row per year; monthly returns one row per payment, up to 600 rows.yearly
loanTermYearsNoLoan term in years. Most US mortgages are 15 or 30.
annualInsuranceNoAnnual homeowners insurance premium in US dollars.
downPaymentPercentNoDown payment as a percentage of the purchase price, 0 to 100. Not a dollar amount.
monthlyExtraPrincipalNoAdditional principal paid each month. Shortens the loan rather than lowering the payment.
propertyTaxRatePercentNoAnnual property tax as a percentage of home value. Omit and pass `state` instead to use that state's average.
annualInterestRatePercentNoAnnual nominal interest rate as a percentage, for example 6.5 for 6.5%.

TDQS

A4.4/5.0
Behavior4/5

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

The description adds useful behavior context beyond the read-only/idempotent annotations, such as the split between principal and interest, the falling balance, and the extra principal payoff feature. It doesn't overpromise or contradict the safe-read nature of the tool.

Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.

Conciseness5/5

Is the description appropriately sized, front-loaded, and free of redundancy?

The description is three concise sentences, front-loaded with the primary purpose, and every sentence adds unique value. No fluff or repetition of schema details.

Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.

Completeness4/5

Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?

With no output schema, the description reasonably explains what the user will get: a payment breakdown, principal/interest split, and balance. It also mentions the extra principal payoff, covering a key feature. It could mention more about the return structure, but for a calculator tool this is adequate.

Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.

Parameters4/5

Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?

Schema coverage is 100%, so the baseline is 3. The description adds extra meaning by explaining the 'granularity' parameter ('monthly' vs 'yearly') and the effect of extra principal, which goes beyond just listing parameter names.

Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.

Purpose5/5

Does the description clearly state what the tool does and how it differs from similar tools?

The description clearly states what the tool does: it provides a payment-by-payment breakdown of a loan, showing the split between principal and interest and the falling balance. It distinguishes itself from sibling tools by focusing on the amortization schedule specifically, not just mortgage calculation or affordability.

Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.

Usage Guidelines4/5

Does the description explain when to use this tool, when not to, or what alternatives exist?

The description provides clear context for when to use each granularity ('monthly' for detail, 'yearly' for overview), but it does not explicitly mention alternatives or when not to use this tool. It is clear enough that this is for amortization schedules, but lacks explicit exclusions or references to sibling tools.

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

All US Mortgage Calculator toolsInspect
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TDQS

A4.5/5.0
Disambiguation5/5

Each tool targets a distinct calculation or information need: affordability, amortization, full mortgage payment, PMI, property tax, refinancing, rent vs buy, loan comparison, closing costs, state rules, and state list. Even overlapping tools like calculate_mortgage and calculate_pmi are clearly separated by depth and purpose.

Naming Consistency5/5

All tool names follow a consistent verb_noun snake_case pattern, using verbs like calculate, compare, estimate, get, and list. The pattern is uniform and predictable across the entire set.

Tool Count5/5

With 11 tools, the server is well-scoped for a US mortgage calculator domain. Each tool covers a meaningful aspect of mortgage analysis without redundancy or bloat.

Completeness5/5

The tool surface covers the full lifecycle of mortgage decision-making: affordability, payment estimation, amortization, PMI, property tax, refinancing, rent vs buy, loan comparison, closing costs, and state-specific rules. No significant gaps are apparent for the stated purpose.

Resources