Financial Math API

POST /api/calc/finance $0.005 per call USDC on Base · x402

Exact financial + token math. POST {op:…}: compound (growth with per-period contributions), amortize (payment, total interest, schedule), npv, irr (deterministic bisection) — and token_units: exact decimal↔base-unit conversion via BigInt for any token decimals (ETH 18, USDC 6), the 18-decimal math that float64 silently corrupts. Iterative series computed exactly, never guessed.

Parameters

Name	In		Description
`op`	body	required	compound \| amortize \| npv \| irr \| token_units
`principal`	body
`rate`	body		annual %, e.g. 6.5
`years`	body
`periods_per_year`	body		default 12
`contribution_per_period`	body
`cashflows`	body		npv/irr — period 0 first
`amount`	body		token_units — decimal or base-unit string
`decimals`	body		token_units — ETH 18, USDC 6
`to`	body		token_units — base \| decimal

Example request

curl -X POST "https://api.webbersites.com/api/calc/finance" \
  -H "Content-Type: application/json" \
  -d '{"op":"amortize","principal":300000,"rate":6.5,"years":30}'
# first call returns 402 + payment requirements; an x402 client pays and retries automatically

Example response

{
    "op": "amortize",
    "payment_per_period": 1896.2,
    "periods": 360,
    "total_interest": 382633.47
}

MCP tool: post_calc_finance — via npx -y webbersites-x402-mcp (local, key stays on your machine) or the remote endpoint https://api.webbersites.com/mcp.

How payment works

There is no signup and no API key. Call the endpoint; it replies 402 Payment Required with machine-readable payment requirements. Your client signs a USDC transfer authorization (EIP-3009, gasless) and retries with the X-PAYMENT header — @x402/fetch does this automatically. See the overview for a working snippet.