--- title: "What Is a Currency API? (Developer Guide, 2026)" description: "A currency API returns exchange rate data over HTTPS in JSON. Guide to how currency APIs work, common endpoints, data sources, use cases, and how to pick one." canonical: https://allratestoday.com/blog/what-is-a-currency-api/ source: AllRatesToday (https://allratestoday.com/) — Markdown mirror of the page above; index of all pages at https://allratestoday.com/llms.txt generated: 2026-10-12T20:43:14.645Z --- ![API technology connections](https://images.pexels.com/photos/16592498/pexels-photo-16592498.jpeg?auto=compress&cs=tinysrgb&dpr=2&h=650&w=940) A **currency API** is a web service that returns exchange rate data to your application over HTTPS, in a machine-readable format (usually JSON). Instead of scraping a website or maintaining your own pipeline of bank feeds, you make a REST request — `GET /rates?source=USD&target=EUR` — and get back the current rate. This guide explains what a currency API does, how it works, common endpoints, real-world use cases, and how to pick the right one. ## What a Currency API Does A currency API sits between your application and the global FX market. It handles: 1. **Data aggregation** — pulling rates from interbank feeds, central banks, and aggregators. 2. **Normalization** — converting varied source formats into a consistent JSON response. 3. **Hosting** — serving rates from infrastructure designed for high availability and low latency. 4. **Access control** — issuing API keys, enforcing rate limits, tracking usage. You call the API, you get a number. The provider handles everything else. ## How a Currency API Works A typical request-response cycle: 1. Your app builds an HTTPS request with: 2. A **source currency** (e.g. `USD`) 3. One or more **target currencies** (e.g. `EUR`, `GBP`) 4. An **API key** (usually in an `Authorization: Bearer ...` header) 5. The provider's server: 6. Authenticates the key 7. Looks up the latest rates from its cache or live feed 8. Returns a JSON response with the rate and a timestamp 9. Your app: 10. Parses the JSON 11. Multiplies the amount by the rate 12. Displays or stores the result Example request: ```bash curl -X GET "https://allratestoday.com/api/v1/rates?source=USD&target=EUR" -H "Authorization: Bearer YOUR_API_KEY" ``` Example response: ```json { "source": "USD", "target": "EUR", "rate": 0.9234, "time": "2026-04-14T12:00:00Z" } ``` ## Common Currency API Endpoints A mature currency API provides several endpoint types, each for a specific job: ### Latest Rates Returns the most recent exchange rates. The bread-and-butter endpoint. ``` GET /api/v1/rates?source=USD ``` ### Historical Rates Returns the rate on a specific past date. Critical for accounting, tax reporting, and backtesting. ``` GET /api/historical-rates?source=USD&target=EUR&date=2024-03-15 ``` ### Time Series Returns a range of daily rates between two dates. Used for trend charts and analysis. ``` GET /api/time-series?source=USD&target=EUR&from=2026-01-01&to=2026-03-31 ``` ### Convert Does the multiplication for you — give it an amount and it returns the converted amount. ``` GET /api/convert?source=USD&target=EUR&amount=100 ``` ### Fluctuation Returns the change, percentage change, and high/low over a period. Useful for rate alerts. ``` GET /api/fluctuation?source=USD&target=EUR&from=2026-04-01&to=2026-04-14 ``` ## Where Currency APIs Get Their Data Not all currency APIs are built on the same data. Understanding the source matters because it determines accuracy and update frequency. - **Interbank feeds** (Reuters/Refinitiv, Bloomberg) — live rates from the actual FX market. Highest accuracy and freshness. Used by AllRatesToday, XE, and institutional providers. - **Central banks** (European Central Bank, Federal Reserve) — one reference rate published per day. Free to use, but daily and limited to ~30 currencies. Used by Fixer and ExchangeRate-API free tiers. - **Aggregators** — blends of multiple sources, with a provider-specific methodology. - **Crypto exchanges** — order-book data from Binance, Coinbase, etc. Used for crypto pairs. An API serving daily ECB data is not "wrong," but it cannot deliver real-time rates no matter how fast its servers are. ## Common Use Cases ### E-Commerce Display prices in the visitor's local currency. Most carts check the rate at cart load and at checkout to avoid surprises. ### SaaS Billing Invoice customers in their own currency while reporting revenue in USD or EUR. Usually calls the API once per invoice generation, not per page load. ### Financial Reporting Convert foreign transactions to a reporting currency at historical rates. Historical endpoint + accounting software. ### Trading and Dashboards Live or near-live rates for charts, screeners, and portfolio trackers. Requires 60-second updates or faster. ### Cross-Border Payouts Marketplaces and payroll systems calculating settlement amounts. Usually combines a currency API with a payment processor. ### Travel and Fintech Apps Consumer-facing converters for travelers, remittance apps, and neobanks. ## What Makes a Good Currency API - **Accurate data source** — interbank feeds beat daily ECB snapshots. - **Update frequency** — real-time (60s) for anything touching money; hourly or daily is fine for reporting. - **Coverage** — at least 150+ fiat currencies, plus metals and crypto if relevant. - **Flat JSON responses** — easy to parse, no nested quotes-object weirdness. - **Official SDKs** — save you writing HTTP plumbing. - **HTTPS and CORS** — table stakes in 2026. - **Transparent pricing** — a real free tier, no hidden fees. - **Good documentation** — working code samples in your language. ## Currency API Pricing Free tiers exist, usually with trade-offs (daily updates, low quotas, restricted base currency). Paid plans run from $10–$100/month for most SaaS needs. Enterprise plans (XE, OANDA) run into thousands per year. For most developers, a free tier is enough to prototype, and a $10–$20/month plan covers production. ## Choosing a Currency API Match the API to the job: - **Indie project / prototype** — AllRatesToday free tier, Frankfurter (no key). - **Production e-commerce / SaaS** — AllRatesToday, Open Exchange Rates, ExchangeRate-API paid plans. - **Trading / fintech** — AllRatesToday (60s) or XE Enterprise. - **Enterprise / regulated** — XE, OANDA, Bloomberg. ## FAQ ### Is there a free currency API? Yes. AllRatesToday, ExchangeRate-API, Open Exchange Rates, and Fixer all offer free tiers. Frankfurter is completely free with no key required. ### What's the difference between a currency API and an exchange rate API? Nothing — they're the same thing. "Currency API," "exchange rate API," "FX API," and "forex API" are used interchangeably. ### Do currency APIs support crypto? Some do (CurrencyFreaks, CurrencyAPI, XE for select coins). Most are fiat-focused. For crypto-heavy work, use a dedicated crypto API like CoinGecko. ### How often do rates update? Depends on the provider and plan. Daily (ECB snapshots) at the low end, 60 seconds on real-time plans, microseconds on institutional feeds. ### Can I use a currency API in the browser? Only if it supports CORS. AllRatesToday and ExchangeRate-API do. Fixer, CurrencyLayer, and XE don't — those require a server-side proxy. ### Do I need a paid plan? For prototypes and low-volume apps, a free tier is fine. For production with live pricing, you'll want a paid plan with at least hourly updates. --- Ready to integrate? [Get a free AllRatesToday API key](https://allratestoday.com/register) — real-time rates, historical data, and official SDKs for JavaScript, Python, and PHP. Try it yourself ``` npm install @allratestoday/sdk ``` ## Ship With Real-Time Rates Real-time mid-market rates, free historical data, 160+ currencies. No credit card required. [Get Your Free API Key](https://allratestoday.com/register) ## Related Articles - [Best Free Currency Exchange API 2026](https://allratestoday.com/blog/best-free-currency-exchange-api-2026/) - [Where Does Exchange Rate Data Come From?](https://allratestoday.com/blog/where-does-exchange-rate-data-come-from/) - [Free vs Paid Exchange Rate APIs](https://allratestoday.com/blog/free-vs-paid-exchange-rate-apis/) - [Best Currency API 2026](https://allratestoday.com/best/best-currency-api-2026/)