APIVerve

Mortgage Calculator

MortgageCalculator

Read-only

Mortgage Calculator: Mortgage Calculator computes monthly and annual loan payments from principal, interest rate, and term. It breaks totals down by principal, interest, property tax, insurance, and HOA dues and returns the loan-to-value ratio, with paid plans adding full amortization schedules, PMI and its removal date, payoff dates, and extra-payment scenarios showing months and interest saved. (Cost: 2 credits)

Tool call template

Replace each placeholder with a value matching the input schema. Only required parameters are included; add optional parameters as needed.

{
  "id": 1,
  "jsonrpc": "2.0",
  "method": "tools/call",
  "params": {
    "arguments": {
      "amount": "<amount>",
      "rate": "<rate>",
      "years": "<years>"
    },
    "name": "MortgageCalculator"
  }
}

Input Schema

Name	Required	Description
`rate`	Yes	The interest rate (percentage)
`years`	Yes	The loan term in years
`amount`	Yes	The loan amount
`pmi_rate`	No	Annual private mortgage insurance rate as a percentage of the loan, charged only when the loan-to-value ratio is above 80%
`annual_hoa`	No	The annual HOA amount
`start_date`	No	Loan start (closing) date; the first payment falls the following month
`downpayment`	No	The down payment amount
`extra_monthly`	No	Extra principal paid every month, to see how much sooner the loan is paid off and how much interest that saves
`annual_propertytax`	No	The annual property tax amount
`annual_homeinsurance`	No	The annual home insurance amount

Output Schema

Name	Required	Description
`data`	No
`error`	No	Error message, null on success
`status`	No	"ok" on success

Schema Changelog

Changes observed during successful MCP inspections.

First observedNov 7, 2026

TDQS

A3.6/5.0

Behavior4/5

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

Annotations only declare a safe read operation, so the description carries the real burden, and it does: it discloses output composition (principal/interest/tax/insurance/HOA split, LTV ratio) and that certain results are gated behind paid plans. The credit cost is also disclosed. It stops short of stating units or the exact shape of the gated fields, but the added context is substantial.

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

Conciseness4/5

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

Effectively one long sentence, but front-loaded with the core function before layering output details and tier gating. The redundant "Mortgage Calculator: Mortgage Calculator" prefix wastes a few words, and the paid-tier clause makes the sentence dense, yet nothing is truly extraneous.

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

Completeness5/5

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

A read-only calculator with 10 fully documented parameters, an output schema, and no destructive semantics needs exactly what's here: what it computes, what it returns, and what is gated. The only plausible gap is sibling disambiguation, which is a routing concern rather than a completeness one.

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

Parameters3/5

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

Schema coverage is 100%, so the schema already documents every parameter, and the description adds little beyond restating the principal/rate/term triple and gesturing at tax, insurance, HOA, PMI, and extra payments. It does hint that extra payments yield months and interest saved, which gives the extra_monthly parameter purpose, but no format or unit detail beyond the schema.

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

Purpose4/5

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

States a specific verb and resource ("computes monthly and annual loan payments from principal, interest rate, and term") and enumerates the output breakdown, so the agent knows exactly what comes back. It never mentions the closely related sibling LoanCalculator or MortgageRate, so differentiation is left to inference.

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

Usage Guidelines2/5

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

No when-to-use or when-not-to-use guidance and no named alternative, despite siblings LoanCalculator and MortgageRate occupying adjacent territory. The only routing signal is an incidental cost note ("Cost: 2 credits"), which isn't usage guidance.

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

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