MCP Server FAQ

A hosted Model Context Protocol (MCP) server at https://mcp.digitalcalculator.info/mcp that exposes 13 financial calculator tools — mortgage, compound interest, 401(k), Social Security, paycheck, IRA, Roth conversion, RMD, HSA, inflation, savings, emergency fund, and loan calculations. Connect it to claude.ai or Claude Desktop via Custom Connectors, use any Streamable HTTP MCP client, or POST JSON-RPC directly. Published by Markcolabs LLC, the company behind DigitalCalculator.info.

Thirteen tools: mortgage_monthly_payment, compound_interest_future_value, retirement_401k_projection (IRS 2026 limits incl. SECURE 2.0 super catch-up), social_security_estimated_benefit (SSA bend-point PIA estimate), paycheck_net_pay (IRS 2026 Percentage Method + FICA + state-aware estimate), ira_contribution_limit, roth_conversion_tax_impact, rmd_distribution_amount, hsa_contribution_limit, inflation_adjusted_value, savings_future_balance, emergency_fund_recommendation, and loan_monthly_payment. All tools return a consistent ToolResult envelope (standardized shape rolling out across all tools in v0.4.x). See the API Reference for full schemas.

Yes — the hosted endpoint is free to use, with no API key and no signup. Note that "free" is not the same as "MIT-licensed": the hosted MCP/API service at mcp.digitalcalculator.info is a Markco Labs–operated commercial service governed by separate hosted-API terms (LICENSE-API.md — acceptable use, rate limits, no warranty). Only the npm package source (@markcolabs/mcp) is MIT-licensed open source — that’s what you self-host, modify, or embed however you want. The HTTP endpoint is rate-limited to 100 requests/minute globally; abusive traffic would saturate the throttle and start returning HTTP 429. See What is the license? for the full distinction.

Use the Custom Connectors UI: open Settings → Connectors → "Add custom connector" and paste https://mcp.digitalcalculator.info/mcp. No authentication is required — the 13 tools appear in your next conversation. This replaces the old local JSON-config stdio setup. See the Quickstart for full setup instructions.

Yes — the endpoint is plain HTTP POST under the hood. Send a JSON-RPC 2.0 tools/call request with the tool name and arguments and you get the ToolResult envelope back in result.content[0].text. A dedicated REST companion API at https://api.digitalcalculator.info/v1/tools/{toolName}/calculate (no JSON-RPC wrapper) is provisioning. See Option 4 of the Quickstart.

Yes. Since the production cutover (ADR-0046), https://mcp.digitalcalculator.info/mcp speaks the MCP Streamable HTTP transport — JSON-RPC 2.0 over HTTP POST with initialize, tools/list, tools/call, resources/list, and resources/read. Claude Custom Connectors and MCP Inspector connect to it directly. If your client only speaks MCP over stdio, the @markcolabs/mcp npm package (v0.4+) is a thin stdio→HTTPS shim to the same endpoint.

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), independent of the package version. Each of the 13 tools carries its own engineVersion. 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 email us so we can prioritize per-key rate limiting.

Email admin@markcolabs.com. 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: email admin@markcolabs.com.

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 the npm version history for all published releases.

MIT for the npm package source — the LICENSE file ships in the npm 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 the MIT LICENSE that ships in the npm package.

The hosted endpoint at https://mcp.digitalcalculator.info/mcp is a separate Markco Labs–operated service. Calls to that URL are additionally governed by separate hosted-API terms (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 13-tool surface at the public throttle level will remain free. If you're interested in B2B / white-label integration today, see /business/ or email admin@markcolabs.com.