Finance

Data source: Standard amortization formulas

MCP Endpoint (Streamable HTTP) https://context.gnist.ai/mcp/mortgage-calculator/

Authentication

All requests require a Gnist-API-Key header (or api_key query parameter).

Free tier: 100 calls/day. Get your API key.

Tools (4)

calculate_monthly_payment
calculate_amortization
calculate_affordability
report_feedback

calculate_monthly_payment

Calculate fixed monthly mortgage payment.

Given a loan amount, interest rate, and term, computes the monthly payment,
total amount paid over the life of the loan, and total interest.

Parameter	Type	Required	Description
`principal`	`number`	required	Loan amount.
`annual_rate`	`number`	required	Annual interest rate as a percentage (e.g. 5.5 for 5.5%).
`term_years`	`integer`	required	Loan term in years.

JSON-RPC Request

{
  "jsonrpc": "2.0",
  "method": "tools/call",
  "id": 1,
  "params": {
    "name": "calculate_monthly_payment",
    "arguments": {
      "principal": 1.0,
      "annual_rate": 1.0,
      "term_years": 1
    }
  }
}

calculate_amortization

Generate a full amortization schedule for a mortgage.

Returns monthly entries showing how each payment splits between principal
and interest, plus the remaining balance after each payment.

Parameter	Type	Required	Description
`principal`	`number`	required	Loan amount.
`annual_rate`	`number`	required	Annual interest rate as a percentage (e.g. 5.5 for 5.5%).
`term_years`	`integer`	required	Loan term in years.

JSON-RPC Request

{
  "jsonrpc": "2.0",
  "method": "tools/call",
  "id": 1,
  "params": {
    "name": "calculate_amortization",
    "arguments": {
      "principal": 1.0,
      "annual_rate": 1.0,
      "term_years": 1
    }
  }
}

calculate_affordability

Estimate how much home a buyer can afford.

Uses the 28% front-end DTI ratio: maximum housing payment is 28% of gross
monthly income, minus existing debts.

Parameter	Type	Required	Description
`annual_income`	`number`	required	Gross annual income.
`annual_rate`	`number`	required	Annual interest rate as a percentage (e.g. 5.5 for 5.5%).
`monthly_debts`	`number`	optional	Existing monthly debt obligations. (default: 0.0)
`down_payment`	`number`	optional	Cash available for down payment. (default: 0.0)
`term_years`	`integer`	optional	Loan term in years. (default: 30)

JSON-RPC Request

{
  "jsonrpc": "2.0",
  "method": "tools/call",
  "id": 1,
  "params": {
    "name": "calculate_affordability",
    "arguments": {
      "annual_income": 1.0,
      "annual_rate": 1.0
    }
  }
}

report_feedback

Report a bug, feature request, or general feedback for this data source.

Use this when something doesn't work as expected, when you'd like
a new feature, or when you have suggestions for improvement.

Args:
feedback: Describe the issue or suggestion.
feedback_type: One of 'bug', 'feature_request', or 'general'.

Parameter	Type	Required	Description
`feedback`	`string`	required
`feedback_type`	`string`	optional	(default: "general")

JSON-RPC Request

{
  "jsonrpc": "2.0",
  "method": "tools/call",
  "id": 1,
  "params": {
    "name": "report_feedback",
    "arguments": {
      "feedback": "example"
    }
  }
}

Quick Start

Shell

curl -X POST "https://context.gnist.ai/mcp/mortgage-calculator/" \
  -H "Content-Type: application/json" \
  -H "Accept: application/json, text/event-stream" \
  -H "Gnist-API-Key: YOUR_API_KEY" \
  -d '{"jsonrpc": "2.0", "method": "tools/call", "id": 1, "params": {"name": "calculate_monthly_payment", "arguments": {"principal": 1.0, "annual_rate": 1.0, "term_years": 1}}}'

Python

import httpx

resp = httpx.post(
    "https://context.gnist.ai/mcp/mortgage-calculator/",
    headers={"Gnist-API-Key": "YOUR_API_KEY", "Content-Type": "application/json"},
    json={
  "jsonrpc": "2.0",
  "method": "tools/call",
  "id": 1,
  "params": {
    "name": "calculate_monthly_payment",
    "arguments": {
      "principal": 1.0,
      "annual_rate": 1.0,
      "term_years": 1
    }
  }
},
)
print(resp.json())