MCP Server FAQ

A hosted Model Context Protocol (MCP) server at https://mcp.digitalcalculator.info/mcp that exposes 9 tools: 8 financial calculator tools — mortgage, compound interest, 401(k), Social Security, paycheck, IRA, Roth conversion, RMD, HSA, inflation, savings, emergency fund, and loan calculations — plus money_flow_map, an interactive money-flow budget map. 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.

9 anonymous tools. Four scenario tools: plan_retirement_income (linked 401(k) + Social Security + SECURE 2.0 RMD picture), evaluate_roth_conversion (2026-bracket tax impact with break-even framing), check_contribution_eligibility (401(k) / Traditional IRA / Roth IRA / HSA limits with phase-outs), and project_growth (nominal + inflation-adjusted growth). Four single-quantity calculators: mortgage_monthly_payment, loan_monthly_payment, paycheck_net_pay (IRS 2026 Percentage Method + FICA + state-aware estimate), and emergency_fund_recommendation. Plus money_flow_map, an interactive money-flow (Sankey) budget map. All tools return the same ToolResult envelope with provenance (rule_year, sources[]); the tools retired in the contract 1.0.0 consolidation remain callable via their REST aliases. See the API Reference for full schemas.

Yes — the anonymous tier is free to use, with no API key and no signup, and it is staying free. 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. Free calls are capped at 500 per UTC day per IP (and 30 per 5-minute window per IP), under a shared 100-requests/minute endpoint throttle. Paid tiers with larger per-key allowances are published on the pricing page. 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 9 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 9 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, UNAUTHORIZED), 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, 401 invalid or revoked Bearer key, 429 rate limit, 500 internal. The response body shape is always single-envelope — never double-nested.

Two layers. Outer: a shared endpoint throttle of 100 requests per minute across all callers (not per-caller), burst 50 — no tier reserves throughput against it. Inner: a per-caller allowance — anonymous callers get 500 calls per UTC day per IP plus a 30-call / 5-minute short-term ceiling; Bearer keys get a per-key daily cap and short-term ceiling by plan (see the rate card). Either layer returns HTTP 429 with retriable: true. The npm package over stdio runs locally and isn't rate-limited.

Yes, with backoff — and read the response headers first. A 429 carries Retry-After plus X-RateLimit-Limit / -Remaining / -Reset; honor Retry-After rather than guessing. A shared-throttle 429 clears within a minute; a per-IP window 429 clears at the next 5-minute boundary; a daily-cap 429 clears at UTC midnight. If you are legitimately hitting the daily cap, that is the signal to move to a Bearer key — or email us and we'll help size the tier.

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), the published rate limits, and a no-warranty disclaimer. If you self-host the source, LICENSE-API.md does not apply to you.

The anonymous tier is free, and we have no plans to change that. Paid tiers already exist for higher per-key allowances, attribution and support — see the rate card — but they buy allowance, identity and support, never different math: authenticated and anonymous responses are byte-identical for the same inputs. If you're interested in B2B / white-label integration, see /business/ or email admin@markcolabs.com.