Real Estate MCP Server

import type { MortgageInput, MortgageResult } from '../types/real-estate.js'; /** * Calculate monthly mortgage payment using standard amortization formula * M = P [ i(1 + i)^n ] / [ (1 + i)^n – 1] * Where: * - M = Monthly payment * - P = Principal (loan amount) * - i = Monthly interest rate * - n = Number of months */ export function calculateMortgage(input: MortgageInput): MortgageResult { // Validate inputs if (input.homePrice <= 0) { throw new Error('Home price must be greater than 0'); } if (input.downPayment < 0) { throw new Error('Down payment cannot be negative'); } if (input.downPayment >= input.homePrice) { throw new Error('Down payment must be less than home price'); } if (input.annualInterestRate < 0) { throw new Error('Interest rate cannot be negative'); } if (input.termYears <= 0) { throw new Error('Loan term must be greater than 0'); } // Calculate loan amount const principal = input.homePrice - input.downPayment; // Calculate monthly interest rate const monthlyInterestRate = input.annualInterestRate / 100 / 12; // Calculate number of payments const numberOfPayments = input.termYears * 12; // Calculate monthly P&I payment let principalAndInterest = 0; if (monthlyInterestRate === 0) { // Handle 0% interest rate case principalAndInterest = principal / numberOfPayments; } else { // Standard amortization formula const factor = Math.pow(1 + monthlyInterestRate, numberOfPayments); principalAndInterest = principal * (monthlyInterestRate * factor) / (factor - 1); } // Calculate monthly property tax const monthlyTax = (input.propertyTaxAnnual || 0) / 12; // Calculate monthly insurance const monthlyInsurance = (input.insuranceAnnual || 0) / 12; // HOA is already monthly const monthlyHOA = input.hoaMonthly || 0; // PMI - typically required if down payment < 20% let monthlyPMI = input.pmiMonthly || 0; if (!input.pmiMonthly && input.downPayment / input.homePrice < 0.20) { // Estimate PMI as 0.5% of loan amount annually if not provided monthlyPMI = principal * 0.005 / 12; } // Calculate total monthly payment const totalMonthlyPayment = principalAndInterest + monthlyTax + monthlyInsurance + monthlyHOA + monthlyPMI; // Calculate a simple APR estimate (doesn't include all fees) // This is a naive calculation - real APR calculation is more complex const totalInterest = (principalAndInterest * numberOfPayments) - principal; const averageBalance = principal / 2; // Rough approximation const aprEstimate = (totalInterest / numberOfPayments / averageBalance) * 12 * 100; return { principalAndInterest: Math.round(principalAndInterest * 100) / 100, monthlyTax: Math.round(monthlyTax * 100) / 100, monthlyInsurance: Math.round(monthlyInsurance * 100) / 100, monthlyHOA: Math.round(monthlyHOA * 100) / 100, monthlyPMI: Math.round(monthlyPMI * 100) / 100, totalMonthlyPayment: Math.round(totalMonthlyPayment * 100) / 100, aprEstimate: Math.round(aprEstimate * 100) / 100 }; } /** * Calculate how much house someone can afford based on monthly payment * @param monthlyPayment Maximum monthly payment * @param downPayment Down payment amount * @param annualInterestRate Annual interest rate (e.g., 6.5 for 6.5%) * @param termYears Loan term in years (e.g., 30) * @returns Maximum home price */ export function calculateAffordability( monthlyPayment: number, downPayment: number, annualInterestRate: number, termYears: number = 30 ): number { // This is the reverse of the mortgage calculation // We'll use the payment to find the max principal const monthlyInterestRate = annualInterestRate / 100 / 12; const numberOfPayments = termYears * 12; let maxPrincipal: number; if (monthlyInterestRate === 0) { maxPrincipal = monthlyPayment * numberOfPayments; } else { const factor = Math.pow(1 + monthlyInterestRate, numberOfPayments); maxPrincipal = monthlyPayment * (factor - 1) / (monthlyInterestRate * factor); } const maxHomePrice = maxPrincipal + downPayment; return Math.round(maxHomePrice); }