Convert real-time currencies
Convert real-time currencies and foreign exchange (Forex) rates anchored to European Central Bank (ECB) base rates. Supports multi-currency target conversions.
Request
- x-api-key: <your-api-key>
- Content-Type: application/json
Response
{
"status": "success",
"from": "EUR",
"to": "PLN",
"amount": 1000,
"rate": 4.2815,
"result": 4281.5,
"asOf": "2026-09-08T09:00:00Z",
"tokensDeducted": 1
}What it does
Converts an amount between any two ISO 4217 currencies at the current mid-market rate and tells you when that rate was fixed. The answer is a number for a dashboard or a quote, not a rate you settle a bank transfer on — it says so in asOf.
When to use it
A price shown in the visitor's currency; a KPI tile that sums revenue across currencies; an invoice preview.
Request
Body
| Field | Type | Required | Description |
|---|---|---|---|
amount | number | no | Amount of money in source currency to convert. |
from | string | no | 3-letter ISO 4217 source currency code (e.g. "USD", "EUR", "GBP", "JPY") |
targets | array<string> | no | Array of target currency codes for multi-currency simultaneous conversion. |
to | string | no | Single 3-letter ISO 4217 target currency code. Overridden if "targets" array is provided. |
Example request
{
"from": "EUR",
"to": "PLN",
"amount": 1000
}Response
| Field | Type | Description |
|---|---|---|
base | object | |
↳ amount | number | |
↳ code | string | |
↳ name | string | |
conversions | object | |
rateDate | string | |
source | string | |
status | string | |
tokensDeducted | integer |
Example response
{
"status": "success",
"from": "EUR",
"to": "PLN",
"amount": 1000,
"rate": 4.2815,
"result": 4281.5,
"asOf": "2026-09-08T09:00:00Z",
"tokensDeducted": 1
}Errors
Every error answers with the same envelope: an HTTP status, a machine code and a sentence.
400 | The body or a parameter failed validation. The details array names the field. |
401 | No key, a revoked key or a wrong header. Send x-api-key. |
402 | The wallet cannot cover this call. Top up or wait for the monthly grant. |
404 | The resource does not exist, or it is not yours. Both answer identically and cost nothing. |
429 | Over the per-minute quota of your tier. Back off and retry. |
5xx | Upstream refused or timed out. The call is not billed. |
Code
curl -X POST 'https://app.castomapi.com/v1/convert/currency' \
-H 'x-api-key: <your-api-key>' \
-H 'Content-Type: application/json' \
-d '{"from": "EUR", "to": "PLN", "amount": 1000}'const res = await fetch('https://app.castomapi.com/v1/convert/currency', {
method: 'POST',
headers: { 'x-api-key': '<your-api-key>', 'Content-Type': 'application/json' },
body: JSON.stringify({"from": "EUR", "to": "PLN", "amount": 1000})
});
const data = await res.json();
console.log(data);import { request } from 'node:https';
// Node 18+ has fetch built in
const res = await fetch('https://app.castomapi.com/v1/convert/currency', {
method: 'POST',
headers: { 'x-api-key': '<your-api-key>', 'Content-Type': 'application/json' },
body: JSON.stringify({"from": "EUR", "to": "PLN", "amount": 1000})
});
const data = await res.json();
console.log(data);import requests
res = requests.post(
'https://app.castomapi.com/v1/convert/currency',
headers={'x-api-key': '<your-api-key>'},
json={"from": "EUR", "to": "PLN", "amount": 1000},
timeout=30,
)
print(res.json())<?php
$ch = curl_init('https://app.castomapi.com/v1/convert/currency');
curl_setopt_array($ch, [
CURLOPT_CUSTOMREQUEST => 'POST',
CURLOPT_RETURNTRANSFER => true,
CURLOPT_HTTPHEADER => ['x-api-key: <your-api-key>', 'Content-Type: application/json'],
CURLOPT_POSTFIELDS => json_encode(['from' => 'EUR', 'to' => 'PLN', 'amount' => 1000]),
]);
$data = json_decode(curl_exec($ch), true);
print_r($data);Cost and limits
This operation costs 1 token. A call that fails is never billed. Every account gets 1000 free tokens a month; paid balances never expire.
Rate limits per minute
| No key | 10 |
| Free | 60 |
| Pro | 300 |
| Enterprise | 1200 |
Questions
What does Convert real-time currencies cost?
1 token per successful call, debited from your wallet after the response. Failed calls are free. Every account receives 1000 free tokens a month.
How do I authenticate?
Send your key in the x-api-key header. One key covers every metered endpoint; there is nothing to enable per endpoint.
Can I send an Authorization: Bearer token instead?
Not for a metered endpoint — those take the x-api-key header and nothing else. Bearer tokens belong to the account side: the dashboard and account APIs accept a JWT session, and castomapi-auth issues those through a standard OAuth2 handshake, with authorization code, client credentials and refresh grants. The auth service page covers it.
What are the limits?
10 requests a minute per IP with no key at all, 60 a minute on the free tier, 300 on Pro, 1200 on Enterprise. Above the no-key tier the quota is per account, across every endpoint.
OpenAPI: https://app.castomapi.com/docs/json