MCP Server FAQ

@markcolabs/mcp is a Model Context Protocol (MCP) server that exposes 5 financial calculator tools — mortgage payment, compound-interest projection, 401(k) projection, Social Security estimated benefit, and paycheck net-pay calculation. Use it from any MCP-compatible client (Claude Desktop, MCP Inspector, agentic CLIs) or call the REST companion endpoint at https://mcp.digitalcalculator.info/mcp directly. Published by Markcolabs LLC, the company behind DigitalCalculator.info.

Five tools: dc.calculator.mortgage.monthlyPayment (monthly P&I, total interest, total paid for a fixed-rate mortgage), dc.calculator.compoundInterest.futureValue (future value, total contributions, interest earned), dc.calculator.retirement401k.projection (year-by-year 401(k) projection with IRS 2026 limits incl. SECURE 2.0 super catch-up), dc.calculator.socialSecurity.estimatedBenefit (SSA bend-point PIA estimate with early/delayed claim math), and dc.calculator.paycheck.netPay (IRS 2026 federal Percentage Method + FICA + simplified state-tax estimate). All tools return a consistent ToolResult envelope. See the API Reference for full schemas.

Yes. MIT-licensed, no API key required, no signup. Use it however you want — personal projects, commercial products, AI agent backends. The HTTP endpoint is rate-limited to 100 requests/minute globally; abusive traffic would saturate the throttle and start returning HTTP 429.

Edit claude_desktop_config.json and add a digitalcalculator entry to mcpServers pointing at node /path/to/@markcolabs/mcp/dist/index.js. Restart Claude Desktop. See the Quickstart for full setup instructions.

Yes — the REST companion API at https://mcp.digitalcalculator.info/mcp is callable with plain HTTP. POST JSON with { "tool": "<tool-name>", "input": {...} } and you get a ToolResult envelope back. Not the MCP wire protocol, but the same tool semantics. See Option 4 of the Quickstart.

No. It is a REST API. Pointing MCP Inspector or Claude Desktop at the HTTP URL will fail handshake. For true MCP, use the npm package over stdio. This is a deliberate v1 decision documented in ADR-0041.

The math matches the corresponding calculators at DigitalCalculator.info to the cent. Parity tests in packages/mcp/test/parity/* enforce this on every release. Where the MCP tool intentionally narrows scope (e.g., paycheck state tax uses a flat 5% estimate rather than per-state bracket tables), the tool description and the methodology.url field explicitly note the limitation.

Yes. Every tool response embeds a canonical YMYL (Your Money or Your Life) disclaimer in the disclaimer field of the result envelope. The same string is exposed as the dc://disclaimers/ymyl MCP resource. Tools never author their own disclaimer text — there's a single source of truth at packages/mcp/src/disclaimers/ymyl.ts. If you're building an agent that quotes the results to users, surface the disclaimer alongside the numbers.

methodology.version is the date of the last substantive update to the methodology document for that calculator. Treat it as a content version for the underlying math. Pair it with engineVersion (the code-side semver) for full audit-trail.

Per-engine SemVer constant that bumps on math changes only (not cosmetic refactors). All 5 engines reset to "1.0.0" in v0.2.0 per ADR-0041. Use it as a cache key.

The error envelope is a single-key JSON object with an error field containing code (one of INPUT_VALIDATION, BUSINESS_RULE, INTERNAL, RATE_LIMIT), message (human-readable), an optional field (for input validation errors), and retriable (boolean; only RATE_LIMIT is retriable). HTTP statuses: 200 success, 400 validation/business-rule, 429 rate limit, 500 internal. The response body shape is always single-envelope — never double-nested.

100 requests per minute globally across all callers (not per-IP). Burst of 50. If you hit it, HTTP 429 with retriable: true. The npm package over stdio runs locally and isn't rate-limited.

Yes, with backoff. The throttle window is one minute; use exponential backoff starting at ~5s. If you're sustained-saturating from a legitimate use case, please open an issue so we can prioritize per-key rate limiting.

Open an issue on the GitHub repo. We triage weekly. Include the tool name, input that reproduces, expected vs actual output, and engineVersion from the response envelope.

Best effort, no SLA. Markcolabs is a small operation; expect ~3–5 business days for triage. Critical issues (security, accuracy regressions) get faster attention.

Per the standard .well-known/security.txt policy at /.well-known/security.txt: open a GitHub issue, or email through the contact form on digitalcalculator.info.

Patch (v0.2.x) covers bug fixes and methodology updates that don't change the tool surface. Minor (v0.x.0) is additive tools or output fields (non-breaking). Major (vX.0.0) is tool renames, removed fields, breaking envelope changes. Tool renames specifically: when a tool name changes (as happened in v0.2.0), the prior version is npm deprecate-d with a clear migration message. See CHANGELOG.md for full version history.

MIT for the npm package source — see LICENSE in the package (added as a standalone file in v0.2.1; copyright "Markco Labs LLC"). Self-host, modify, redistribute, embed in commercial products — all permitted. Attribution to "DigitalCalculator.info" or "Markco Labs LLC" is appreciated for AI/agent quotes but not required.

Two surfaces, two license documents. The npm package source (@markcolabs/mcp) is MIT — you can npm install it, run it over MCP stdio on your own machine, modify it, or deploy your own copy. That use is governed only by LICENSE.

The hosted endpoint at https://mcp.digitalcalculator.info/mcp is a separate Markco Labs–operated service. Calls to that URL are additionally governed by LICENSE-API.md (added in v0.2.1) — covering acceptable use (no scraping, no resale of raw output, no sole-authority financial decisions), a 100-req / 5-min per-IP WAFv2 throttle, and a no-warranty disclaimer. If you self-host the source, LICENSE-API.md does not apply to you.

Yes for v1.x. We may introduce a paid tier later for higher rate limits, custom domain hosting, white-label deployments, or per-customer API keys — but the existing 5-tool surface at the public throttle level will remain free. If you're interested in B2B / white-label integration today, see /business/ or contact us through the site.