Mortgage calculations for AI agents

What agents can do

11 tools, each a pure function over published data. Every result carries the assumptions behind it and a disclaimer, so an agent can explain where a figure came from.

• calculate_mortgage

  Calculate a monthly mortgage payment

  Full monthly housing cost for a US mortgage: principal and interest, property tax, homeowners insurance, mortgage insurance and HOA dues, plus lifetime totals and payoff timing.

• calculate_amortization

  Build an amortization schedule

  Payment-by-payment breakdown of how a loan is repaid, showing the split between principal and interest and the falling balance.

• calculate_pmi

  Calculate mortgage insurance

  Mortgage insurance for any US loan programme, including the upfront charges most calculators omit.

• calculate_property_tax

  Estimate property tax

  Annual and monthly property tax for a home, using a state's average effective rate.

• calculate_affordability

  Work out how much house someone can afford

  Maximum affordable home price from income, existing debt payments and available down payment, using the 28/36 qualifying ratios.

• calculate_refinance

  Evaluate a refinance

  Whether refinancing is worth it: the new payment, monthly saving, and how many months it takes to recover closing costs.

• estimate_closing_costs

  Itemise closing costs

  Line-by-line buyer closing costs — lender fees, title, appraisal, transfer taxes, prepaid escrow — plus total cash needed at the table including the down payment.

• calculate_rent_vs_buy

  Compare renting with buying

  Compares renting and buying on net wealth rather than on monthly payment, accounting for equity, appreciation, maintenance, selling costs, and the return a renter earns on money not spent on a down payment.

• compare_loans

  Compare loan options side by side

  Compares two to five loan scenarios and reports which is cheapest by monthly payment and which by lifetime cost, separately, because they frequently are not the same loan.

• get_state_mortgage_rules

  Look up a state's property tax rules

  How property tax actually works in one state: how assessed value is derived, any statutory growth cap, the billing cycle, named exemptions such as homestead, the filing deadline, who hears appeals and the window to file, notable county variation, and a link to the state's own tax authority.

• list_states

  List all 50 states with property tax rates

  Every US state with its average effective property tax rate, median home value and estimated annual tax.

Available resources

Read-only context an agent can pull in to answer responsibly.

• usmc://company/profile

  Publisher profile

  Who operates the service, how it is funded, editorial policy, data sources and known limitations.

• usmc://glossary

  Mortgage glossary

  Definitions for US mortgage and property tax terms, with acronyms expanded and common misreadings called out.

• usmc://states/index

  All 50 states

  Every state with its average effective property tax rate, median home value and dataset provenance.

• usmc://states/{state}

  State tax rules

  Assessment basis, growth caps, exemptions, billing cycle, appeal route and county variation for one state.

• usmc://assumptions/rates

  Published assumptions

  Every rate, fee and limit the calculations rely on, each with its source and the year it applies to.

• usmc://legal/disclaimer

  Legal disclaimer

  Scope and limits of the estimates, and what this service is not.

• usmc://docs/openapi

  REST specification

  The OpenAPI 3.1 document, for callers who would rather use HTTP than MCP.

Agent prompts

Discoverable prompts that chain the right tools in the right order and carry the caveats through to the answer.

• explain_my_payment

  Explain a monthly payment

  Break a payment into its parts and say which will rise over time.

• compare_fha_vs_conventional

  Compare FHA with conventional

  Weigh the two, including the upfront and long-run mortgage insurance costs.

• estimate_closing_costs

  Estimate cash to close

  Itemise closing costs and separate what is negotiable from what is not.

• how_much_can_i_afford

  Work out an affordable price

  Derive a price range from income and debts, and name the binding constraint.

• should_i_refinance

  Evaluate a refinance

  Assess break-even against lifetime cost, which frequently disagree.

• explain_amortization

  Explain amortization

  Show why early payments are mostly interest and what extra principal does.

• first_time_buyer_walkthrough

  First-time buyer walkthrough

  Chain affordability, closing costs, payment and mortgage insurance in order.

Connect

A remote server, so there is nothing to install and no key to obtain — point a client at the URL and the tools appear.

claude mcp add --transport http \
  usmortgagecalc https://www.usmortgagecalc.com/mcp

{
  "mcpServers": {
    "usmortgagecalc": {
      "type": "http",
      "url": "https://www.usmortgagecalc.com/mcp"
    }
  }
}

{
  "mcpServers": {
    "usmortgagecalc": {
      "url": "https://www.usmortgagecalc.com/mcp"
    }
  }
}

{
  "servers": {
    "usmortgagecalc": {
      "type": "http",
      "url": "https://www.usmortgagecalc.com/mcp"
    }
  }
}

npx @modelcontextprotocol/inspector https://www.usmortgagecalc.com/mcp