FIX API vs REST API – What to Choose When Integrating With Crypto Markets?

If you have an app or software for which you want to collect data from multiple cryptocurrency markets or want to trade crypto on many exchanges simultaneously, this article is a perfect fit for you. Inside, we will explain what the REST API, WebSocket, and FIX API are and how they are used to retrieve data. We will also help you choose between them depending on your needs.

API, FIX API, REST API – explaining key concepts

An API (Application Programming Interface) is a set of rules, protocols, and tools that allow different software applications to communicate with each other. It can be compared to a universal remote control that allows you to control various devices (TV, DVD player, sound system) without knowing their internal workings. Similarly, API lets your application interact with different services or databases without the need to understand their complex internal processes. The buttons on the remote are like API endpoints, each performing a specific function when pressed.

In the context of cryptocurrency exchanges:

• APIs help developers integrate exchange functionality into their applications or systems
• They provide a standardized way to access exchange features programmatically
• APIs enable automated trading, data analysis, portfolio management, and more

What is REST API?

Introduced in 2000, REST API (Representational State Transfer) is a versatile architectural style for designing networked applications. It uses standard HTTP methods for communication, typically represented as URLs, making it easy to implement and widely adopted by cryptocurrency exchanges for various operations.

The key characteristics of REST APIs include:

1. Universality
   Suitable for a wide range of applications, including web and mobile apps.
2. Statelessness
   Each request from client to server must contain all the information needed to understand and process the request.
3. Client-Server Architecture
   The client and server are separate entities that communicate over HTTP.
4. Uniform Interface
   Resources are identified in requests, typically using URLs. The server transfers representations of resources to the client.
5. Layered System
   A client cannot ordinarily tell whether it is connected directly to the server or through intermediaries.

In the context of cryptocurrency exchanges, REST APIs are commonly used for various operations such as:

• Retrieving market data (prices, order books, trade history)
• Placing, modifying, or canceling orders
• Managing user accounts and balances
• Accessing historical data

REST APIs typically use JSON or XML for data formatting, making them easy to work with in most programming languages. They’re popular due to their simplicity, scalability, and compatibility with existing web infrastructure.

FIX API

FIX API (Financial Information eXchange) is a high-performance protocol designed for real-time exchange of financial information. Developed in 1992, it’s widely used in the securities trading industry and has found application in cryptocurrency markets for high-frequency trading. Especially since it stands out for its low-latency communication. FIX API uses a tag-value pair format for messages, where each piece of information is identified by a numerical tag.

In the context of cryptocurrency markets, FIX API is used for:

• High-frequency trading operations
• Direct market access
• Real-time market data streaming
• Complex order types and algorithmic trading

FIX API is more complex to implement than REST API, but it offers advantages in terms of speed and crypto data standardization. It’s particularly favored by institutional investors and high-volume traders who require rapid execution and can handle its complexity.

While not as widely adopted in the crypto space as REST APIs, several major cryptocurrency exchanges now offer FIX API access to cater to institutional clients and advanced traders.

How does WebSocket differ from FIX API?

WebSocket, standardized in 2011, is a protocol enabling full-duplex, real-time communication between client and server over a single TCP connection. In the context of cryptocurrency exchanges, WebSocket is particularly useful for streaming live market data and receiving instant updates on trades and order books. While FIX API excels in low-latency, high-volume scenarios, and REST API offers flexibility and ease of use for general-purpose integration, WebSocket bridges the gap by providing real-time capabilities with relatively simple implementation, making it popular for building responsive trading interfaces and algorithms in the crypto space.

FIX API vs REST API vs WebSocket – a comparison

See a comparison of all three protocols divided into several main areas.

Market Data Integration

Real-time updates:

• REST API: Limited (polling required)
• WebSocket: Excellent (push-based)
• FIX API: Good (can be near real-time)

Data volume handling:

• REST API: Good for small to medium volumes
• WebSocket: Excellent for high volumes
• FIX API: Excellent for high volumes

Latency:

• REST API: Higher
• WebSocket: Low
• FIX API: Very low

Historical data retrieval:

• REST API: Excellent
• WebSocket: Limited
• FIX API: Limited

Ease of implementation:

• REST API: Easy
• WebSocket: Moderate
• FIX API: Complex

Trading Integration

Order placement:

• REST API: Good
• WebSocket: Good
• FIX API: Excellent

Order modification & cancellation:

• REST API: Good
• WebSocket: Good
• FIX API: Excellent

Trade execution speed:

• REST API: Moderate
• WebSocket: Fast
• FIX API: Very fast

Complex order types:

• REST API: Supported
• WebSocket: Supported
• FIX API: Highly supported

Scalability for high-frequency trading:

• REST API: Limited
• WebSocket: Good
• FIX API: Excellent

General Characteristics

Connection type:

• REST API: Stateless
• WebSocket: Stateful
• FIX API: Stateful

Protocol:

• REST API: HTTP/HTTPS
• WebSocket: WebSocket
• FIX API: FIX

Data format:

• REST API: Usually JSON
• WebSocket: Usually JSON
• FIX API: FIX (tag-value pairs)

Firewall-friendly:

• REST API: Yes
• WebSocket: May require configuration
• FIX API: May require configuration

Language/platform support:

• REST API: Universal
• WebSocket: Wide
• FIX API: Specialized

Typical use case:

• REST API: General-purpose integration
• WebSocket: Real-time data streaming
• FIX API: High-frequency trading

REST API, FIX API, WebSocket – what to choose?

The choice between REST API, WebSocket, and FIX API depends on your specific use case. Let’s break down the four scenarios that might suit your requirements.

You need historical crypto market data

For historical data, REST API is ideal because it allows you to make specific requests for large amounts of data efficiently. You can easily query for particular periods or specific cryptocurrencies without maintaining a constant connection.

Reasons:

• Well-suited for large data requests
• Allows for specific queries with parameters (date ranges, specific assets)
• Efficient for non-real-time data retrieval

You need real-time market data

In this case, WebSocket and the FIX API are applicable, but we recommend WebSocket. It provides a continuous stream of data without the need for repeated requests, making it more efficient than constantly polling a REST API. This is crucial for keeping order books, price charts, and other live data up-to-date.

Reasons:

• Provides continuous, real-time data stream
• Efficient for receiving frequent updates (e.g., price changes, order book updates)
• Lower overhead compared to constant REST API polling

You need to place simple orders and sell cryptocurrencies

For simple orders and offers, REST API is typically sufficient. It’s widely supported, easy to implement, and well-suited for operations that don’t require split-second timing. Most exchanges provide comprehensive REST APIs for basic trading operations.

Reasons:

• Straightforward implementation for basic operations
• Widely supported by most exchanges
• Suitable for lower-frequency trading

You perform advanced trading operations

Advanced trading operations like high-frequency trading (HFT) and statistical arbitrage benefit most from FIX API. Its low latency and support for complex order types make it ideal for these scenarios. However, FIX API is not always available or necessary for all advanced trading. In such cases, a combination of WebSocket (for real-time data) and REST API (for order execution) can be a good alternative.

Reasons:

• Optimized for low-latency communication
• Supports complex order types
• Industry-standard for high-frequency trading

Alternative: WebSocket (if FIX is not available)

• Provides real-time data necessary for algorithmic trading
• Can be used in conjunction with REST API for order placement

Why not have them all?

When you want access to multiple cryptocurrency exchanges, usually the biggest challenge is the time-consuming integration process. Therefore, the best solution is to choose an API provider, like CoinAPI, that will give you access to hundreds of crypto markets through one simple connection. This way, you don’t have to worry about which protocol a particular exchange uses. Meanwhile, the above comparison between REST, FIX, and WebSocket may come in handy when choosing the best plan for your needs.

Check out the Market Data API for historical and real-time data.

Try the EMS Trading API if you want to trade.

We also encourage you to read REST API and FIX API documentation.