Agents can’t lend. They can call it.

GET /v1/amortization HTTP/1.1
host: apis.finance

HTTP/1.1 200
{
  "object": "schema",
  "resource": "https://apis.finance/v1/amortization",
  "sku": "Amortization math",
  "status": "LIVE",
  "callable": true,
  "price": "$0 · keyless",
  "price_note": "Posted, flat, fixed at post. Zero is a posted price and it binds. No key, no registration, no payment rail, no 402.",
  "method": "POST",
  "request_content_type": "application/json",
  "description": "A level-payment amortization schedule computed from the numbers you supply. Pure math: no upstream, no stored input, no Application, no Decision, no advice.",
  "request": {
    "principal": {
      "type": "number",
      "required": true,
      "unit": "currency major units",
      "minimum": 0.01,
      "maximum": 1000000000000,
      "note": "The financed amount. Rounded to cents on receipt."
    },
    "annual_rate_pct": {
      "type": "number",
      "required": true,
      "unit": "percent per year, nominal, compounded monthly",
      "minimum": 0,
      "maximum": 100,
      "note": "6.5 means 6.5%, not 0.065. Zero is accepted and yields a straight-line schedule."
    },
    "term_months": {
      "type": "integer",
      "required": true,
      "minimum": 1,
      "maximum": 600,
      "note": "Number of level payments."
    },
    "start_date": {
      "type": "string",
      "required": false,
      "format": "YYYY-MM-DD",
      "note": "First payment due date. When present, every period carries a due_date; when absent, periods are numbered only. Day-of-month is clamped to the length of each month."
    }
  }
}

POST /v1/amortization HTTP/1.1
host: apis.finance
content-type: application/json

{ "principal": -1 }

HTTP/1.1 422
{
  "object": "error",
  "type": "invalid_request",
  "status": 422,
  "resource": "https://apis.finance/v1/amortization",
  "message": "This request does not describe a computable schedule. 3 fields must change.",
  "errors": [
    {
      "field": "principal",
      "code": "out_of_range",
      "message": "principal is outside the range this row computes.",
      "expected": "number between 0.01 and 1000000000000",
      "received": -1
    },
    {
      "field": "annual_rate_pct",
      "code": "missing",
      "message": "annual_rate_pct must be a finite JSON number expressed in percent per year. 6.5 means 6.5%, not 0.065.",
      "expected": "number between 0 and 100",
      "received": null
    },
    {
      "field": "term_months",
      "code": "missing",
      "message": "term_months must be a whole number of monthly payments.",
      "expected": "integer between 1 and 600",
      "received": null
    }
  ],
  "cure": {
    "route": "SELF",
    "needs_human": false,
    "description": "Correct every field named in errors[] and call again. Nothing here is reserved to a licensed party, so no routing clears this: the request is the only thing that has to change.",
    "schema": "GET https://apis.finance/v1/amortization"
  },
  "charge": null,
  "note": "No schedule was served. No record, no charge. This row is keyless and posted at $0, so nothing was metered either way."
}