REST calculation API

The REST calculation API runs your calculators from your own servers. You send inputs as JSON and get results, tables and a disclaimer back.

Before you start

You need:

• A secret API key. Create one in the portal under API keys. A secret key starts with sk_.
• The API host. The Go live page in the portal shows it.
• At least one calculator group on your cobrand. Calling a calculator outside your groups gives a 403.

attention

Use secret keys on your servers only. Never put a secret key in browser code, a mobile app or source control. Browsers use the embed endpoints with a public key instead. The API sends no CORS headers, so a browser can't call it.

Minimal example

Set the host and key, then ask for a calculation:

export AZTEC_API_HOST="<your API host>"
export AZTEC_SECRET_KEY="<your secret key>"

curl -sS -X POST "https://$AZTEC_API_HOST/v1/calculators/auto-loan-payment/calculate" \
  -H "Authorization: Bearer $AZTEC_SECRET_KEY" \
  -H "Content-Type: application/json" \
  -d '{"inputs":{"vehiclePrice":30000,"downPayment":3000,"tradeInValue":0,"salesTaxRate":6,"apr":7,"termMonths":60},"locale":"en-US"}'

The response looks like this:

{
  "calculatorKey": "auto-loan-payment",
  "engineVersion": "1",
  "calculatedAt": "2026-01-15T12:00:00+00:00",
  "results": { "monthlyPayment": 566.02, "totalInterest": 8274.3 },
  "tables": [
    {
      "key": "schedule",
      "label": "Amortization schedule",
      "columns": [
        { "key": "month", "label": "Month", "type": "integer" },
        { "key": "balance", "label": "Balance", "type": "currency" }
      ],
      "rows": [{ "month": 1, "balance": 27650.19 }]
    }
  ],
  "disclaimer": "Educational use only, not financial advice.",
  "inputsUsed": { "vehiclePrice": 30000, "downPayment": 3000, "tradeInValue": 0, "salesTaxRate": 6, "apr": 7, "termMonths": 60 }
}

Show the disclaimer text with every result you display.

Operations

All operations are under /v1/calculators and need the header Authorization: Bearer <secret key>.

Operation	Request	Returns
List calculators	GET /v1/calculators	An array of the calculators your cobrand can use: key, name, group and category
Get calculator schema	GET /v1/calculators/{calculatorKey}/schema	The inputs and results of one calculator
Calculate	POST /v1/calculators/{calculatorKey}/calculate	The results, tables and disclaimer

Use the schema operation to find each input's key, type, range, allowed values and default. Inputs you leave out take their default, and inputsUsed shows the values the engine used.

Options

The calculate request body is a JSON object with these properties:

Property	Required	Description
inputs	Yes	An object of input values by input key. The engine ignores properties that aren't inputs of the calculator.
locale	No	en-US, es-US, en-CA or fr-CA. The default is your cobrand's default locale. Any other value is a validation_failed error.

The response always carries your engine version in the engineVersion field and in the Aztec-Engine-Version header. See Engine versions.

Errors and limits

Errors use the application/problem+json format. Each error has type, title, status, detail, instance, a stable code and a traceId. Branch on code, not on detail. Validation errors also carry an errors array.

Status	code	Meaning
400	malformed_json	The body isn't a JSON object.
400 or 422	validation_failed	One or more inputs are invalid. Business calculators answer 400. All other calculators answer 422.
401	unauthorized	The key is missing, revoked or not a secret key. The response has WWW-Authenticate: Bearer.
403	calculator_not_entitled	Your cobrand doesn't have this calculator's group.
404	calculator_not_found	No active calculator has this key.
413	payload_too_large	The body is over 64 KB.
429	rate_limited	You went over your request limit. Wait the number of seconds in Retry-After.
500	engine_fault	The calculation failed. Quote the traceId to support.
503	catalog_unavailable	The calculator catalog can't be read right now.
503	cobrand_resolution_unavailable	The service can't verify the key right now.
503	engine_version_unavailable	The engine version your cobrand uses isn't loaded.
503	engine_timeout	The calculation took more than 10 seconds.
503	engine_overloaded	The engine is busy.

Retry a 503 after a short wait. Don't retry a 4xx other than 429 without changing the request.

Each item in the errors array of a validation error has field, code and a message in English. Some items also have min and max. The field code is one of required, invalid_type, below_min, above_max, invalid_step, invalid_option, unsupported_locale, invalid, too_many_items, out_of_range, not_whole_number, nothing_to_finance, price_not_above_variable_cost, target_margin_too_high, payment_below_interest or payoff_too_long.

Limit	Value
Request body	64 KB
Calculation time	10 seconds
Request rate	600 requests a minute for each cobrand, shared with the MCP endpoint. See Rate limits.
Caching	Every response has Cache-Control: no-store.

Related API reference

• Calculate
• Get calculator schema