Financial calculators for AI agents

A free Model Context Protocol (MCP) server with 5 deterministic calculator tools. Use from Claude Desktop, MCP Inspector, agentic CLIs, or call the REST endpoint directly. No signup, no API key, MIT-licensed.

Read the Quickstart →

What this is

The Model Context Protocol (MCP) is an open standard that lets AI tools call structured backends. Our MCP server exposes 5 financial calculations as MCP tools so an AI agent can answer questions like "what's my monthly mortgage payment on $400k at 6.5%" with consistent, math-checked answers backed by IRS 2026 limits and SSA bend points — not LLM-hallucinated arithmetic.

Every response carries a YMYL disclaimer, a methodology link, and a versioned engine ID so downstream agents can quote results with full provenance.

Available tools (v0.2.1)

• Mortgage payment — Monthly P&I, total interest, total paid for a fixed-rate mortgage. dc.calculator.mortgage.monthlyPayment
• Compound interest — Future value with optional monthly contributions; configurable compounding frequency. dc.calculator.compoundInterest.futureValue
• 401(k) projection — Year-by-year balance projection honoring IRS 2026 limits including SECURE 2.0 super catch-up. dc.calculator.retirement401k.projection
• Social Security — SSA bend-point PIA estimate with early-claim reduction and delayed credit. dc.calculator.socialSecurity.estimatedBenefit
• Paycheck net pay — IRS 2026 federal Percentage Method + FICA + simplified state estimate. dc.calculator.paycheck.netPay
• Disclaimer resource — Canonical YMYL disclaimer exposed as an MCP resource for agent-side quoting. dc://disclaimers/ymyl

How to connect

Claude Desktop

npm install -g @markcolabs/mcp then add the server to claude_desktop_config.json. Tools appear in the next conversation. Full steps →

MCP Inspector

For debugging: npx @modelcontextprotocol/inspector node $(npm root -g)/@markcolabs/mcp/dist/index.js. Browser UI for every tool. Full steps →

HTTP REST

No MCP client? POST JSON to https://mcp.digitalcalculator.info/mcp. Same tool semantics over plain HTTP. Full steps →

A request, end-to-end

Mortgage payment on $300,000 at 6.5% for 30 years:

curl -X POST https://mcp.digitalcalculator.info/mcp \
  -H 'Content-Type: application/json' \
  -d '{"tool":"dc.calculator.mortgage.monthlyPayment","input":{"principal":300000,"annualRatePercent":6.5,"termYears":30}}'

Returns HTTP 200 with the structured envelope every tool uses:

{
  "result": { "monthlyPayment": 1896.20, "totalInterest": 382633.47, "totalPaid": 682633.47 },
  "disclaimer": "Estimates only — for educational purposes...",
  "methodology": { "url": "https://www.digitalcalculator.info/mortgage-calculator/", "version": "2026-05-09" },
  "calculatedAt": "2026-05-23T18:42:11.123Z",
  "engineVersion": "1.0.0"
}

See the API Reference for per-tool schemas, output shapes, and error codes.

Why use it

• Always Free — No sign-up, no API key, no usage limits on the npm package. The HTTP endpoint has a 100 req/min throttle but no per-user metering.
• Quote-Safe — Every response carries a canonical YMYL disclaimer and methodology link. Agents can quote results with full audit trail.
• Parity-Tested — Math matches the corresponding calculators at digitalcalculator.info to the cent. Tested via Vitest parity suite.
• Open License — MIT-licensed npm package (see LICENSE). Embed in commercial agents, internal tools, or AI products without restriction. Hosted endpoint additionally governed by LICENSE-API.md (rate limits, acceptable use, no-warranty). Self-hosting the source is unaffected.

Next steps

• Quickstart — Install + first call in under 5 minutes
• API Reference — Full schemas, output shapes, error codes for each tool
• FAQ — Accuracy, YMYL posture, rate limits, support, change policy
• npm package — Source, CHANGELOG, version history
• GitHub repo — Open issues, contribute