UK Mortgage Repayment MCP

Tool-only MCP server for estimating UK repayment mortgage payments in ChatGPT.

Build and run locally (no ngrok)

You can develop and test both the MCP server and browser front end entirely on your machine. No public URL or tunnel is needed.

Prerequisites

• Node.js 22 or later (node --version)

• npm

Install the root dependencies once:

npm install

Install the front-end dependencies once:

cd test-client
npm install
cd ..

1. Start the MCP server

In the repository root, run:

npm run dev

The server listens at:

http://localhost:8787/mcp

Use PORT=9000 npm run dev to choose a different port.

Leave this terminal running.

2. Start the local front end and chat API

Open a second terminal in the repository root and run:

cd test-client
npm run dev

This starts the browser UI on port 5173 and the local chat-orchestrator API on port 5174. The browser and orchestrator are local; generating chat replies uses OpenRouter and needs your API key and internet access.

Before starting it, create test-client/.env if it does not already exist:

OPENROUTER_API_KEY=your_api_key

Open http://127.0.0.1:5173/. The default MCP endpoint is http://127.0.0.1:8787/mcp. You can use both the chat composer and the MCP Connect control.

Direct MCP controls only (no chat)

If you specifically want to test only MCP JSON-RPC calls and do not need the chat composer or an OpenRouter key, run this instead:

cd test-client
npm run dev:ui

Use the MCP Connect control in this mode to inspect the available server tools. The chat composer requires the local port-5174 API and will fail if used with dev:ui. See the test-client README for model and endpoint settings.

Related MCP server: Real Estate MCP Server

Tools

calculate_mortgage_repayment

Inputs:

• loanAmount: mortgage loan amount in pounds sterling

• annualInterestRatePercent: nominal annual interest rate, for example 5.25

• termYears: whole mortgage term in years

• monthlyOverpayment: optional extra monthly repayment in pounds sterling

Outputs include monthly payment, total paid, total interest, and overpayment impact when provided.

find_mortgage_product_rates

Inputs:

• propertyValue: property value in pounds sterling

• loanAmount: borrowing amount in pounds sterling

• termYears: mortgage term from 2 to 40 whole years

• depositAmount: optional; if supplied, it must equal property value minus borrowing

It generates illustrative 2/3/5-year fixed and 2-year tracker products from the calculated LTV band. Each result includes the initial rate, monthly repayment, product fee, estimated APRC, reversion rate, and maximum LTV. These are deterministic demo calculations, not live rates, availability, eligibility, or offers.

mortgageNeed is optional and defaults to switch_residential. The supported values are switch_residential, first_time_buyer, move_home, remortgage, buy_to_let, remortgage_buy_to_let, and switch_buy_to_let. It records the selected customer journey; every journey uses the same deterministic illustrative pricing algorithm.

get_customer_support

Inputs:

• topic: general (default) or mortgage

Outputs include official-source-linked HSBC UK contact options and phone numbers. The values are a local snapshot for the test tool; use the returned official contact page as the source of truth for current details and opening hours. General support output also includes HSBC's contact/chat guidance and online-banking links.

Using ChatGPT developer mode

ChatGPT's hosted service cannot reach 127.0.0.1 or localhost on your computer. Therefore, without a public HTTPS endpoint, use the local browser client or MCP Inspector to develop and test the server. Connecting the MCP directly to ChatGPT developer mode requires a publicly reachable HTTPS URL; this repository does not require ngrok for local development.

Verify

npm test
npm run build
npm run typecheck

You can also test the MCP endpoint with the MCP Inspector:

npx @modelcontextprotocol/inspector@latest --server-url http://localhost:8787/mcp --transport http

The calculation is an estimate for illustration only and is not financial advice.