Inputs
| Field | Type | Valid domain |
|---|---|---|
| loanAmount | float | 10,000 – 2,000,000 |
| termMonths | int | 120 – 480 |
| fixedRate | float | 0.005 – 0.15 |
| armInitialRate | float | 0.001 – 0.15 |
| armInitialPeriodMonths | int | 12 – 120 |
| armAdjustedRate | float | 0.005 – 0.2 |
- armInitialPeriodMonths must be ≤ termMonths − 12 (the adjustment happens at least a year before payoff); violating requests are rejected, never adjusted.
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/arm-vs-fixed
{
"loanAmount": 1005000,
"termMonths": 300,
"fixedRate": 0.08,
"armInitialRate": 0.08,
"armInitialPeriodMonths": 66,
"armAdjustedRate": 0.1
}Response (chart arrays compacted)
{
"ok": true,
"model": "arm-vs-fixed",
"specVersion": "1.0.0",
"contractUrl": "/api/v1/models/arm-vs-fixed",
"specUrl": "/api/v1/models/arm-vs-fixed/spec",
"inputs": {
"loanAmount": 1005000,
"termMonths": 300,
"fixedRate": 0.08,
"armInitialRate": 0.08,
"armInitialPeriodMonths": 66,
"armAdjustedRate": 0.1
},
"outputs": {
"fixedPayment": 7756.753004698706,
"armInitialPayment": 7756.753004698706,
"armAdjustedPayment": 8928.498496486076,
"balanceAtAdjustment": 917747.8714397141,
"fixedTotalInterest": 1322025.9014096116,
"armTotalInterest": 1596214.3464878565,
"initialMonthlySavings": 0,
"paymentShockDelta": 1171.7454917873702,
"lifetimeDelta": 274188.4450782449
},
"sentinels": [],
"assumptions": [
"Implements model spec arm-vs-fixed v1.0.0 (dual-implementation verified).",
"armInitialPeriodMonths must be ≤ termMonths − 12 (the adjustment happens at least a year before payoff); violating requests are rejected, never adjusted."
],
"facts": [],
"record": {
"sha256": "afa891ccc969714446dafc9260975031dcf9a054bb3c63a2ec38e8fc0385e485",
"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.