Inputs
| Field | Type | Valid domain |
|---|---|---|
| balance | float | 500 – 100,000 |
| apr | float | 0.05 – 0.36 |
| minPaymentPct | float | 0.01 – 0.05 |
| minPaymentFloor | float | 15 – 50 |
| fixedPayment | float | 25 – 5,000 |
- minimumNeverPaysOff / fixedNeverPaysOff (booleans) are the authoritative never-pays-off signals; when true, that path's months and interest are truncated at the 1200-month horizon — never compare months to 1200.
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/credit-card-minimum
{
"balance": 50000,
"apr": 0.21,
"minPaymentPct": 0.03,
"minPaymentFloor": 33,
"fixedPayment": 2500
}Response (chart arrays compacted)
{
"ok": true,
"model": "credit-card-minimum",
"specVersion": "1.0.0",
"contractUrl": "/api/v1/models/credit-card-minimum",
"specUrl": "/api/v1/models/credit-card-minimum/spec",
"inputs": {
"balance": 50000,
"apr": 0.21,
"minPaymentPct": 0.03,
"minPaymentFloor": 33,
"fixedPayment": 2500
},
"outputs": {
"monthsMinimum": 167,
"interestMinimum": 28940.737017951156,
"minimumNeverPaysOff": false,
"monthsFixed": 25,
"interestFixed": 12080.378878598758,
"fixedNeverPaysOff": false,
"monthsSaved": 142,
"interestSaved": 16860.3581393524
},
"sentinels": [],
"assumptions": [
"Implements model spec credit-card-minimum v1.0.0 (dual-implementation verified).",
"minimumNeverPaysOff / fixedNeverPaysOff (booleans) are the authoritative never-pays-off signals; when true, that path's months and interest are truncated at the 1200-month horizon — never compare months to 1200."
],
"facts": [],
"record": {
"sha256": "b029efdc010055eca4fa3c38ea1792f583a372f5ee5a3790ecedef20d4d19635",
"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.