Financial calculators for AI agents

A free hosted Model Context Protocol (MCP) server with 13 deterministic calculator tools, live at https://mcp.digitalcalculator.info/mcp (Streamable HTTP, POST, no auth). Connect from claude.ai or Claude Desktop in under a minute via Custom Connectors. No signup, no API key.

Read the Quickstart →

What this is

The Model Context Protocol (MCP) is an open standard that lets AI tools call structured backends. Our hosted MCP server exposes 13 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 (13)

Mortgage payment — Monthly P&I, total interest, total paid for a fixed-rate mortgage. mortgage_monthly_payment
Compound interest — Future value with optional monthly contributions; configurable compounding frequency. compound_interest_future_value
401(k) projection — Year-by-year balance projection honoring IRS 2026 limits including SECURE 2.0 super catch-up. retirement_401k_projection
Social Security — SSA bend-point PIA estimate with early-claim reduction and delayed credit. social_security_estimated_benefit
Paycheck net pay — IRS 2026 federal Percentage Method + FICA + state-aware tax estimate. paycheck_net_pay
IRA contribution limit — 2026 eligible IRA contribution with age-50+ catch-up and Roth MAGI phase-out. ira_contribution_limit
Roth conversion — Federal tax impact of a single Roth conversion using 2026 brackets, with break-even years. roth_conversion_tax_impact
RMD amount — 2026 required minimum distribution via the IRS Uniform Lifetime Table, with missed-RMD penalty info. rmd_distribution_amount
HSA contribution limit — 2026 HSA limit by HDHP coverage tier with age-55+ catch-up and employer-contribution offset. hsa_contribution_limit
Inflation adjustment — Future-dollar equivalent or purchasing-power erosion over N years. inflation_adjusted_value
Savings balance — Future savings balance with monthly deposits and monthly compounding. savings_future_balance
Emergency fund — Personalized emergency-fund target and savings timeline by household situation. emergency_fund_recommendation
Loan payment — Monthly payment and total interest for any fixed-rate amortizing loan. loan_monthly_payment

Plus two MCP resources: the canonical YMYL disclaimer (dc://disclaimers/ymyl) and a methodology-URL manifest (dc://methodologies/manifest) for agent-side quoting.

How to connect

Claude Custom Connectors (recommended)

In claude.ai or Claude Desktop: Settings → Connectors → "Add custom connector", then paste https://mcp.digitalcalculator.info/mcp. No authentication required — tools appear in your next conversation. Full steps →

MCP Inspector

For debugging: npx @modelcontextprotocol/inspector, choose the Streamable HTTP transport, and connect to https://mcp.digitalcalculator.info/mcp. Browser UI for every tool. Full steps →

npm shim (stdio-only clients)

If your MCP client only speaks stdio, npx @markcolabs/mcp runs a thin local shim that forwards stdio JSON-RPC to the hosted HTTPS endpoint. Full steps →

Raw HTTP / REST

No MCP client? POST JSON-RPC directly to https://mcp.digitalcalculator.info/mcp from any HTTP client. A REST companion API at https://api.digitalcalculator.info/v1/tools/{toolName}/calculate is provisioning. Full steps →

A request, end-to-end

Mortgage payment on $300,000 at 6.5% for 30 years, as an MCP tools/call:

curl -X POST https://mcp.digitalcalculator.info/mcp \
  -H 'Content-Type: application/json' \
  -d '{"jsonrpc":"2.0","id":1,"method":"tools/call","params":{"name":"mortgage_monthly_payment","arguments":{"principal":300000,"annualRatePercent":6.5,"termYears":30}}}'

Returns a JSON-RPC envelope whose result.content[0].text is the structured tool result 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": "2026-06-02T18:42:11.123Z",
  "engineVersion": "1.0.0"
}

This standardized response envelope is rolling out across all 13 tools in v0.4.x. See the API Reference for per-tool schemas, output shapes, and error codes.

Why use it

Always Free — No sign-up, no API key. The hosted endpoint is rate-limited to keep it healthy for everyone, but there is 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 (the LICENSE ships in the npm package). Embed in commercial agents, internal tools, or AI products without restriction. The hosted endpoint is additionally governed by separate hosted-API terms (LICENSE-API.md — rate limits, acceptable use, no-warranty). Self-hosting the source is unaffected.

Next steps

Quickstart — Connect + first call in under 5 minutes
API Reference — Full schemas, output shapes, error codes for all 13 tools
Versioning & Deprecation Contract — Semver rules, 90/180-day notice windows, anonymous-parity guarantee (P14 O2-KR1)
Changelog — Release history + three-axis version model; we ship continuously without breaking integrations
Status — Published operational snapshot: endpoint operational, 13 tools live, anonymous-parity green
Pricing — Anonymous free tier plus Developer, Business, and Enterprise API plans
API key onboarding — How to request a key and integrate, end to end
FAQ — Accuracy, YMYL posture, rate limits, support, change policy
npm package — stdio shim, CHANGELOG, version history
Contact & support — Questions, feedback, integration help

Support

Found a bug, need help integrating, or want to show off what you built? Email admin@markcolabs.com.