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MCP Loan Calculator in Claude Desktop

Monthly payments and full amortization in one sentence. loan_payment returns the monthly payment and total interest for principal, rate and term, and loan_amortize returns the full schedule; the annuity formula is implemented exactly, a 0% rate is handled as straight-line division rather than producing NaN, and every amount passes the shared money formatter so the cents agree with a bank's.

The client for the couch conversation: mortgage math happens away from the desk, and the payment plus total interest comes back before the other tab would have loaded the calculator site with its banner ads.

What you get in Claude Desktop

You say	Tool
Monthly payment on a 320,000 mortgage at 5.5% over 25 years?	`loan_payment`
Amortize that loan and show year 3.	`loan_amortize`
Compare 15 vs 30 years at 6.2% on 200,000.	`loan_payment, twice`

The contract suite asserts the annuity arithmetic over real stdio against hand-computed values: a 320,000 loan at 5.5% over 25 years returns the same monthly payment to the cent in both tools, the amortization schedule's principal and interest columns sum to the payment on every row, and the final balance lands on zero.

Install it in Claude Desktop

The file is claude_desktop_config.json, and the key inside it is mcpServers.

Scope	Path
macOS	`~/Library/Application Support/Claude/claude_desktop_config.json`
Windows	`%APPDATA%\Claude\claude_desktop_config.json`

One click, with no JSON. Download loan-calculator.mcpb from the latest release and open it. Claude Desktop installs it as an extension and runs it on the Node runtime it ships with, so neither your PATH nor your node version comes into it, and there is no file to edit. Everything below is the manual route, for when you want the entry in the config file itself.

The config block, which needs both strings absolute:

{
  "mcpServers": {
    "loan-calculator": {
      "command": "node",
      "args": ["/absolute/path/to/mcp-servers/servers/loan-calculator/dist/index.js"]
    }
  }
}

If node came from nvm, asdf or homebrew, use the absolute path that which node prints rather than the bare word, because a stdio server started by this app inherits a limited PATH:

"command": "/Users/you/.nvm/versions/node/v22.14.0/bin/node"

The node command above wants a built file. From a clone, once:

git clone https://github.com/theluckystrike/mcp-servers.git
cd mcp-servers && npm install
npm run build -w packages/mcp-license -w servers/loan-calculator

That writes servers/loan-calculator/dist/index.js, and its absolute path is the one argument the config needs.

The npm packages are not published yet, so the form below returns a 404 today. It is here because it is what the entry becomes the day the publish lands, with nothing else changed:

{
  "mcpServers": {
    "loan-calculator": {
      "command": "npx",
      "args": ["-y", "@theluckystrike/mcp-loan-calculator"]
    }
  }
}

Save, then completely quit Claude Desktop and start it again. A window reload is not enough.

Nothing is published to npm yet, so the working install paths are the ones above: the .mcpb bundle from the latest release, a clone and build, or the hosted URL.

No install: the hosted endpoint

There is no hosted endpoint for this one yet. MCP Loan Calculator runs locally over stdio with the config above, which is also the only form in which it reads and writes files on your own disk. Thirty of the servers in this collection are served at https://mcp.zovo.one/mcp/<name> over MCP streamable HTTP; https://mcp.zovo.one/mcp/connect lists them and prints a ready URL for each.

Claude Desktop notes worth knowing first

Two documented facts decide whether the entry works: every path in claude_desktop_config.json must be absolute, and a stdio server started here inherits only a limited, platform-dependent subset of environment variables. If node came from nvm or homebrew, paste what `which node` prints instead of the bare word. The .mcpb route avoids both: Claude Desktop ships a built-in Node.js environment.

Free: Everything: two tools, no metering, no key. Pro is $19 once, verified offline.

Questions

Where is claude_desktop_config.json?

macOS: ~/Library/Application Support/Claude/claude_desktop_config.json. Windows: %APPDATA%\Claude\claude_desktop_config.json. There is no published Linux path. Settings, Developer, Edit Config opens the right copy and creates it if it does not exist.

I added it and MCP Loan Calculator does not appear.

In order: did you fully quit and restart, not just close the window? Is every path absolute? And is the command resolvable, given the limited environment a stdio server inherits here? If node came from nvm, paste what which node prints.

Can I install it without editing JSON?

Yes. An .mcpb bundle, the format renamed from .dxt, opens with Claude and shows an installation dialog. One you built yourself goes in through Settings, Extensions, Advanced settings, Install Extension.

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