Inputs
| Field | Type | Valid domain |
|---|---|---|
| currentBalance | float | 1,000 – 2,000,000 |
| annualRate | float | 0.001 – 0.3 |
| remainingTermMonths | int | 6 – 480 |
| extraMonthlyPayment | float | 0 – 10,000 |
All fields required. Out-of-domain values are rejected with per-field errors — never clamped. Unknown fields are rejected.
Live example — generated from the real engine
Request
POST /api/v1/models/extra-payment
{
"currentBalance": 1001000,
"annualRate": 0.15,
"remainingTermMonths": 243,
"extraMonthlyPayment": 5000
}Response (chart arrays compacted)
{
"ok": true,
"model": "extra-payment",
"specVersion": "1.0.0",
"contractUrl": "/api/v1/models/extra-payment",
"specUrl": "/api/v1/models/extra-payment/spec",
"inputs": {
"currentBalance": 1001000,
"annualRate": 0.15,
"remainingTermMonths": 243,
"extraMonthlyPayment": 5000
},
"outputs": {
"basePayment": 13155.36,
"basePayoffMonths": 243,
"acceleratedPayoffMonths": 95,
"baseTotalInterest": 2195736.9337578616,
"acceleratedTotalInterest": 706864.9496822625,
"monthsSaved": 148,
"interestSaved": 1488871.9840755991
},
"sentinels": [],
"assumptions": [
"Implements model spec extra-payment v1.0.0 (dual-implementation verified)."
],
"facts": [],
"record": {
"sha256": "33a8429c2d849dc8eab6a81ad5b8b8867c4bd0185f4ffbf2860d7f549ca42bc6",
"fields": [
"model",
"specVersion",
"inputs",
"outputs"
],
"howToVerify": "Store this record with any advice or agent output built on these numbers. To verify later: build {model, specVersion, inputs, outputs} from the stored response, serialize as JSON with object keys sorted recursively (no whitespace), and SHA-256 it — a match proves the numbers came from this spec version with these inputs, unaltered."
},
"disclaimer": "Illustrative planning model, not financial advice. Outputs follow the published model spec exactly; read the spec for assumptions and exclusions before relying on any number."
}This example is executed against the production engine when the page builds — it cannot drift from the API's real behavior.