Developer API

Every calculator.
As an API.

Deterministic, validated, JSON in / JSON out. Every tool in the fleet is available as a single POST endpoint — the same math the web UI uses, no side effects, no auth on localhost.

How it works

Endpoint

POST https://calcfleet.com/api/v1/tools/{slug}
Content-Type: application/json

Replace {slug} with any tool slug from the catalog below. Send the tool's input fields as a JSON body; every field is validated server-side with Zod before the calculation runs.

Responses

  • 200Successful computation — { result: … }
  • 400Invalid input — { error, issues } with per-field Zod issues
  • 404Unknown slug
  • 403Forbidden — missing or invalid API key

Production access runs through RapidAPI — subscription manages authentication and rate limits. Available on RapidAPI soon.

For AI agents (MCP)

Free during launch

CalcFleet is a Model Context Protocol (MCP) server — the deterministic math engine for AI agents. Every calculator in the fleet is exposed as an MCP tool over Streamable HTTP, so assistants like Claude can run precise, Zod-validated financial and practical calculations instead of guessing the arithmetic. No API key, no side effects, same math the web UI uses. All 32 tools are available automatically.

Endpoint

https://calcfleet.com/api/mcp   (Streamable HTTP)

Connect

{
  "mcpServers": {
    "calcfleet": {
      "url": "https://calcfleet.com/api/mcp"
    }
  }
}

Add this to your agent's MCP configuration (Claude Desktop, Claude Code, or any MCP-compatible client). Tool names mirror the slugs below with dashes as underscores — e.g. compound_interest_calculator.

Full example

Mortgage overpayment — $200,000 at 5% over 30 years with $200/month extra. Numbers match the web calculator.

Request

POST /api/v1/tools/mortgage-overpayment-calculator
Content-Type: application/json

{
  "principal": 200000,
  "annualRatePct": 5,
  "termYears": 30,
  "extraMonthly": 200
}

Response 200

{
  "result": {
    "monthlyPayment": 1073.64,
    "baselineMonths": 360,
    "withExtraMonths": 256,
    "monthsSaved": 104,
    "baselineTotalInterest": 186511.57,
    "withExtraTotalInterest": 125351.06,
    "interestSaved": 61160.51,
    "schedule": [
      { "month": 1, "interest": 833.33, "principalPaid": 440.31, "balance": 199559.69 },
      { "month": 2, "interest": 831.50, "principalPaid": 442.14, "balance": 199117.55 },
      { "month": 3, "interest": 829.66, "principalPaid": 443.98, "balance": 198673.57 }
    ]
  }
}

Schedule truncated to 3 of 256 rows — the full response includes every amortization row.

Endpoint catalog

32 endpoints

All endpoints follow the same pattern. New tools added to the fleet appear here automatically.

Custom integrations or volume needs? partnership@calcfleet.com