OpenCurrencyRates (Currency Exchange/ Currency Converter API)

🌍 Simple Currency API

A lightweight hobby project built with NestJS to demonstrate caching, dynamic currency conversion, and REST API design.

✨ Free to use for learning, college projects, or personal experiments!
⚠️ Hosted on Render’s free tier — don’t expect high uptime or speed 😄

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✨ Key Features

✅ Real-time exchange rates 🌍 Country metadata 🔗 Free and open-source

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🚀 Endpoints

Currencies Metadata

• Method: GET
• Path: /api/currencies
• Description: Returns metadata for all supported currencies (name, symbol).

Example request:
https://opencurrencyrates.onrender.com/api/currencies

Example response:

{
    "time_last_update_unix": 1760832151,
    "time_next_update_unix": 1760920141,
    "data": [
        {
            "countryName": "United States",
            "countryCode": "US",
            "symbol": "$",
            "flag": "🇺🇸",
            "currency": "USD"
        },
        {
            "countryName": "United Arab Emirates",
            "countryCode": "AE",
            "symbol": "د.إ",
            "flag": "🇦🇪",
            "currency": "AED"
        },
    ]
}

Exchange Rates by Base Currency

• Method: GET
• Path: /api/currency/:base
• Description: Returns exchange rates relative to the given base currency (e.g., INR, EUR).

Example request:
https://opencurrencyrates.onrender.com/api/currency/INR

/api/currency/:base endpoint supports two optional query parameters for flexible responses:

• metadata=true → includes extra metadata.
• currencies=INR,USD,SGD,... → returns rates only for the specified currencies.

Example request:
https://opencurrencyrates.onrender.com/api/currency/GBP?metadata=false&currencies=INR,HKD

Example response:

{
    "base": "GBP",
    "time_last_update_unix": 1760832151,
    "time_next_update_unix": 1760920381,
    "data": {
        "HKD": 10.43,
        "INR": 118.145
    }
}

✅ To show country's flag in UI, use country code from metadata and put it in FlagAPI e.g. https://flagsapi.com/IN/flat/64.png
✅ Any currency can be used as base
✅ Rates updated once per day (cached to reduce cost)

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Usage

cURL

curl "https://opencurrencyrates.onrender.com/api/currency/USD?currencies=INR,EUR"

Python

import requests

api_url = "https://opencurrencyrates.onrender.com/api/currency/USD"
params = {
    "currencies": "INR,EUR"
}

response = requests.get(api_url, params=params)

if response.status_code == 200:
    data = response.json()
    print(data)
else:
    print(f"Error: {response.status_code}")

Kotlin (with Fuel)

import com.github.kittinunf.fuel.httpGet
import com.github.kittinunf.result.Result

fun main() {
    val apiUrl = "https://opencurrencyrates.onrender.com/api/currency/USD"
    val params = listOf("currencies" to "INR,EUR")

    apiUrl.httpGet(params).responseString { _, _, result ->
        when (result) {
            is Result.Success -> {
                val data = result.get()
                println(data)
            }
            is Result.Failure -> {
                val ex = result.getException()
                println(ex)
            }
        }
    }
}

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💡 How It Works

• The app fetches exchange rate data from a public free-tier API.
• Responses are cached to disk using cache-manager-fs-hash, ensuring the upstream API is called only once per 24 hours — even after cold starts on Render.
• Built with NestJS and deployed on Render’s free tier.

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🛠️ For Developers

Feel free to:

• Use this API in college assignments, side projects, or demos.
• Study the code: modular NestJS structure, file-based caching, dynamic base conversion.
• Fork and extend it!

🔒 Please be kind: This runs on a free Render instance. Avoid aggressive polling or high-volume requests.

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📈 Need Professional Exchange Rates?

For production-grade applications (fintech, e-commerce, etc.), consider these reliable services:

• Open Exchange Rates
• ExchangeRate-API
• CurrencyAPI
• Fixer.io

They offer higher rate limits, historical data, webhooks, and SLA-backed uptime.

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🙌 Made With

• NestJS
• cache-manager-fs-hash
• Render

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🎓 Built as a learning exercise — hope it helps you too!
— Happy coding 💻

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