# frankfurter.historical

**stable** **Standard**

ECB reference rates on a past date.

`GET /v1/frankfurter/historical`

## What you get

One Frankfurter record in Onekey's unified shape, in `data`. If the record does not exist you get a `404 not_found` and are not charged.

## What it costs

- **Standard · 1 credit** for a fresh fetch, charged only when it succeeds.
- **Free when served from cache (0.2 credit for a cached response over 100 KB).**
- **Free** if the request is invalid (never charged) or the source fails or reports not found (refunded).

## Parameters

| Name | Type | Required | Default | What it is | Constraints |
| --- | --- | --- | --- | --- | --- |
| `date` | string | yes | (required) | Date YYYY-MM-DD | max 10 chars; must match `\d{4}-\d{2}-\d{2}`; trimmed |
| `base` | string | no | `eur` | Base currency (ISO 4217), e.g. usd | max 3 chars; must match `[A-Za-z]{3}`; trimmed, lowercased |

## Request

```bash
curl "https://api.onekey.dev/v1/frankfurter/historical?date=2024-01-02&base=usd" \
  -H "x-api-key: YOUR_API_KEY"
```

```python
import requests

res = requests.get(
    "https://api.onekey.dev/v1/frankfurter/historical",
    params={"date": "2024-01-02", "base": "usd"},
    headers={"x-api-key": "YOUR_API_KEY"},
)
body = res.json()

if body["success"]:
    print(body["data"])
else:
    print(body["error"]["code"], body["error"]["message"])
```

```javascript
const params = new URLSearchParams({ date: "2024-01-02", base: "usd" });
const res = await fetch(`https://api.onekey.dev/v1/frankfurter/historical?${params}`, {
  headers: { "x-api-key": "YOUR_API_KEY" },
});
const body = await res.json();

if (body.success) console.log(body.data);
else console.error(body.error.code, body.error.message);
```

## Recorded response

A real Frankfurter response, recorded and returned in Onekey's shape. Fields the platform does not provide are `null`.

```json
{
  "success": true,
  "data": {
    "market": {
      "symbol": "USD"
    },
    "entity": {
      "date": "2024-01-02T00:00:00Z"
    },
    "ext": {
      "amount": 1,
      "rates": {
        "AUD": 1.4738,
        "BGN": 1.7851,
        "BRL": 4.8888,
        "CAD": 1.3294,
        "CHF": 0.84931,
        "CNY": 7.1435,
        "CZK": 22.533,
        "DKK": 6.8046,
        "EUR": 0.91274,
        "GBP": 0.79085,
        "HKD": 7.8139,
        "HUF": 348.76,
        "IDR": 15524,
        "ILS": 3.624,
        "INR": 83.32,
        "ISK": 137.55,
        "JPY": 142.1,
        "KRW": 1313.23,
        "MXN": 17.058,
        "MYR": 4.6025,
        "NOK": 10.2971,
        "NZD": 1.5947,
        "PHP": 55.66,
        "PLN": 3.9894,
        "RON": 4.5368,
        "SEK": 10.1812,
        "SGD": 1.3265,
        "THB": 34.285,
        "TRY": 29.726,
        "ZAR": 18.5889
      }
    }
  },
  "metadata": {
    "platform": "frankfurter",
    "endpoint": "historical",
    "cached": false,
    "stale": false,
    "age_s": 0,
    "fetched_at": "2026-01-01T12:00:00+00:00",
    "credits_charged": 1,
    "request_id": "7f3a9c2e5b1d4c8fa2e6d0b9c4f18e37"
  },
  "error": null
}
```

## Field mapping

How this endpoint's source fields become Onekey's [unified schema](https://onekey.dev/docs/schema.md). Fields the source lacks come back as `null`.

| Source path | Onekey field | Transform |
| --- | --- | --- |
| `base` | `market.symbol` | - |
| `date` | `entity.date` | `toIsoDate` |
| `amount` | `ext.amount` | `toNumber` |
| `rates` | `ext.rates` | - |

## Caching and freshness

- Fresh for about 1 hour. Repeat calls in that window are served from cache and are free.
- Between 1 hour and 1 day the cached copy is still served instantly and marked `stale: true` while Onekey refreshes it in the background.
- If the source is down when a refresh is needed, the last copy can be served for up to 1 day more (marked stale).
- A "not found" is remembered for 5 minutes and is free.
- The cache is shared across all customers, which is what keeps repeat calls cheap.

## What can go wrong

| Status | Code | What to do |
| --- | --- | --- |
| 401 | `unauthorized` | Check the `x-api-key` header. |
| 402 | `insufficient_credits` | [Add credits](https://onekey.dev/pricing); your balance must cover the price. |
| 404 | `not_found` | That record does not exist. Free; do not retry. |
| 422 | `invalid_params` | Fix the parameters using the table above. Free. |
| 429 | `rate_limited` | Wait `Retry-After` seconds, then retry. |
| 502 | `upstream_error` | The source failed. Refunded; retry with backoff. |

See [Errors](https://onekey.dev/docs/errors.md) for the full list and retry guidance.

Status: stable (verified against the live source).