Socket.IO vs. WebSocket: Key differences and which to use

WebSocket is an industry standard that describes a way for clients and servers to exchange messages in realtime. It is accompanied by an API that enables access to that protocol. That’s a crucial difference compared to Socket.IO which, as we’ll see later, is a fully featured messaging library.

The WebSocket API, supported by most modern browsers, extends the protocol to web clients, providing methods to create WebSocket objects, manage connections, send and receive messages, and handle events triggered by the WebSocket server. For more information on WebSockets and how the protocol works, you can read our piece The WebSocket API and protocol explained.

But what role, exactly, does WebSocket play in our application infrastructure? To find out, let’s look at WebSocket's key features, advantages, and disadvantages.

• Two-way communication: WebSocket connections are full duplex, meaning that messages go in both directions between client and server, without blocking each other.

• Persistent connections: WebSocket keeps the connection open for as long as you need it, or until something such as a network issue disrupts it. That changes how you think about working with messages, as it becomes an ongoing resource.

• Widespread support: As a web standard technology, WebSocket is available just about everywhere, such as browsers, backend languages, and IOT devices.

• Focuses on delivery of discrete messages: WebSocket deals in self-contained messages. For example, a chat message from one participant to everyone else in a particular chat group. A message is either delivered or not. That’s in contrast with streaming protocols, like WebRTC, where dropping individual parts of the data (for example, a few frames in a video) is acceptable if it helps to maintain the flow of bytes.

• Low latency: Everything about WebSocket is designed to minimize latency. There’s only one connection to create, meaning each subsequent message saves the overhead associated with creating a fresh HTTP connection. But it’s not just about the overhead of setting up the connection. WebSocket message headers are as small as 2 bytes each, compared to hundreds of times that size for HTTP.

• Implementation flexibility: Because WebSocket is a protocol, rather than a messaging library, it puts relatively few restrictions on how you build your application. For example, different parts of your application could be written in different languages, so long as they use compliant WebSocket libraries.

• Supports different message formats: How you encode your messages is up to you. WebSocket is only interested in delivering them. So, you could choose a compact binary to reduce latency to an absolute minimum or human-readable JSON.

• It’s just a protocol: WebSocket is a standard, not an implementation. That means you’ll need to choose a library, like ws, Python’s websockets, or a richer messaging library like Socket.IO, to build with. If you choose a pure WebSocket implementation, you’ll need to implement functionality such as connection monitoring and messaging guarantees that aren’t covered by the WebSocket specification.

• You have to manage your own infrastructure: One of the biggest challenges in implementing realtime communication using WebSocket is building out and maintaining the infrastructure to ensure your users experience minimal latency, high uptime, and consistent message delivery.

• No automatic reconnections: WebSocket itself doesn’t monitor connection status nor does it automatically reconnect when something goes wrong. That’s logic you’d have to write yourself, if you choose a pure WebSocket implementation.

• Blocked connections: Even though WebSockets generally benefit from widespread support, certain environments (such as corporate networks with proxy servers) will block WebSocket connections.

• Limited message guarantees: WebSocket’s data integrity guarantees are quite weak. It doesn’t guarantee message delivery or that a message will be delivered exactly once. This is something you’d need to build yourself.

• Scaling can be hard: As a stateful protocol, horizontally scaling WebSocket to multiple servers can be complex. You’ll need additional logic, and potentially a single point of failure in the form of a database, to enable sticky sessions between individual servers and clients.

Socket.IO is a realtime messaging library for JavaScript developers that is based on WebSocket. Just like WebSocket, it offers low latency, full duplex messaging - but rather than only specifying a standard, Socket.IO gives you both a client and a backend library to use in your applications.

It’s worth noting that Socket.IO isn’t API compatible with WebSocket. That’s because it builds on the functionality defined in the WebSocket spec with the aim of giving you everything you need to build realtime communication into your applications.

We’ve already looked in some detail at WebSocket. So, how does Socket.IO compare?

• Open source library: Socket.IO comes in two parts - a JavaScript library for the client side, and a NodeJS library for the server. Using them, you can implement realtime messaging in your app with relatively little effort. If you’re working in a backend language other than JavaScript/NodeJS, then there are libraries with varying levels of support.

• Can use HTTP long polling if WebSocket is unavailable: Socket.IO’s transport layer, Engine.IO, first establishes each connection using HTTP long polling. It then upgrades to WebSocket if it’s available. Recent versions of Socket.IO also introduced support for WebTransport, which is an HTTP/3 realtime communication protocol with limited availability in major browsers. By selecting the connection method, Socket.IO saves you some work, as otherwise you’d need to write your own code to handle situations where WebSocket is unavailable.

• Event-driven: Socket.IO lets your application define and respond to custom events. For example, you can create events for user actions such as message sent, user typing, or file uploaded and hook-up your application to respond as needed.

• Message-based: As with WebSocket, Socket.IO works at the message level, where the integrity of each individual message is important. That also means that it’s not a good fit for streaming video or audio, just like WebSocket.

• Connection management: When a connection is interrupted, Socket.IO automatically attempts to reconnect according to the connection strategy that you decide, such as how long it should wait before trying again and how many reconnection attempts it should make.

• Rooms: Rooms allow you to group multiple clients together in one channel, so you can broadcast a message to all of them with just one call to Socket.IO.

• Multiplexing: Socket.IO’s namespacing lets you divide a single connection into multiple logical connections, which can help you to organize and manage separately the communication for different parts of your application. This is likely to be more resource efficient than running multiple WebSocket connections, especially as it removes the overhead of establishing multiple connections. However, features such as multiplexing mean Socket.IO is generally less performant that pure WebSocket.

• Reduces your development and maintenance overhead: As a realtime messaging library, Socket.IO takes care of a lot of functionality that you would otherwise have to implement yourself if you were using a pure WebSocket implementation, for example, falling back to HTTP if WebSocket is unavailable, reconnecting disrupted connections automatically, and multiplexing.

• You still need to build the infrastructure: Socket.IO makes it easier to implement realtime communication in your code (and you can now build a chat platform off of their sample chat project), but you still need to build and maintain the backend infrastructure. 

• Single region: Socket.IO can only run in one data center or cloud region. With no fallback, failures at your cloud provider will take your messaging offline. Driving all traffic to a single geographic location also means users further away will experience higher latencies. In cases where uptime and reliability are critical, consider using a realtime PaaS that has a global network, instead.

• Weak message guarantees Socket.IO defaults to 'at most once' delivery. In other words, it promises never to deliver your message more than once - but it doesn't rule out the chance of the message not being delivered at all. That’s largely the same with WebSocket, which relies on TCP’s ordering to deliver messages in order but offers no other guarantees. For anything else, you’ll need to implement it in your application code, whether it’s Socket.IO or WebSocket.

• Not a drop-in replacement for WebSocket: Socket.IO does not set out to be a pure WebSocket library. Instead, it can use WebSocket as one transport for delivering messages. That lets Socket.IO innovate, with some of the additional features we’re covered such as multiplexing, gives you additional functionality, but it does mean you can’t easily switch to another messaging library. That could cause issues if you have non-JavaScript clients, for example.

• Favors the JavaScript ecosystem: If you’re working with something other than NodeJS on your backend, Socket.IO offers secondary implementations for languages such as Java and Rust. However, each of those libraries is playing catch-up with the JavaScript versions and will, most likely, drag behind in terms of features and quality. 

For a more detailed introduction to Socket.IO, you can read our piece Socket.IO: How it works, when to use it, and how to get started.

Choosing between Socket.IO and WebSocket isn’t completely straightforward as their offerings are fundamentally different: . Socket.IO is a fully featured messaging library, whereas WebSocket works at a much lower level and requires that you implement more of the functionality yourself.

Choosing the right solution to implement your application’s realtime communication comes down to:

• Customization

• Developer experience, including languages and frameworks

• Scalability, reliability, and guarantees

• Performance

Let’s look at them in turn.

Choosing Socket.IO means balancing ease of use with flexibility. It simplifies development by automating transport selection and offering richer features including multiplexing. That allows you to put more effort into what makes your app unique. 

However, this ease comes at a cost: if Socket.IO's design choices don't align with what you need, then you could spend more time fighting its design choices than if you chose a more appropriate alternative. If you want more customization, you need to work at a lower level of abstraction. WebSocket is one way to do that but there are other protocols, libraries, and platforms to consider. 

The choice you make hinges on your team’s resources, project timelines, and your philosophy as a developer. Do you value complete control over the technology stack, crafting each component to fit your precise vision? Or would you rather use existing solutions to get to market faster, even if it means less scope for customization?

Key takeaway: if customizability is your priority, then WebSocket wins over Socket.IO. 

Socket.IO and WebSocket set out to achieve fundamentally different things with their developer experience: Socket.IO builds on top of WebSocket to give you conveniences that make implementing realtime messaging easier, whereas WebSocket is a lower-level standard for ongoing, two-way communication.

As a native JavaScript and NodeJS library, Socket.IO gives you an idiomatic and familiar approach to delivering realtime communication. The quality of its documentation and the breadth of its developer community also mean the learning curve should be relatively shallow.

Where you’ll hit problems with Socket.IO is if you have non-JavaScript components in your application stack. For example, your backend might be in Java, .NET, or Ruby on Rails. To get a more Socket.IO-like experience, you’ll need to use a messaging library for that language or framework, such as Spring, SignalR, or Rails’ ActionCable. None of those, though, are compatible with Socket.IO.

However, if you build your own messaging functionality on top of pure WebSocket libraries, like Node’s ws, then the developer experience will vary from one library to another.

Key takeaway: Developer experience will depend on your stack, but Socket.IO offers an easy learning curve and robust documentation if you are working primarily with Javascript and NodeJS.

The features of a messaging library or protocol are only part of the story. Once you’re in production, its ability to scale, stay online, and deliver your data reliably come into focus.

Depending on your needs, this is where both Socket.IO and WebSocket lose some points:

• Scalability:

  • Socket.IO: Out of the box, Socket.IO scales vertically. Add more memory, CPU, and network bandwidth and you’ll be able to handle more traffic. Research shows an individual server handling 10,000 concurrent connections, but that’s dependent on the shape of the traffic and the capacity of the server. Scaling out, by adding more servers, becomes more complicated. You’ll need a load balancer and a persistence layer to keep track of which clients are connected to which server.

  • WebSocket: Similarly, scaling WebSocket depends on whether you’re looking at vertical or horizontal scaling. Adding more capacity to a single server is straightforward but you’ll eventually hit diminishing returns for ever higher costs. Horizontal scaling is possible but, again, you’ll need a way to keep track of which sessions belong to which server and to balance load amongst those servers.

• Reliability: Scalability and reliability are two sides of the same coin. If you can scale horizontally, you improve your chances of withstanding the failure of some part of your infrastructure. The primary limitation for both Socket.IO and WebSocket is that they are designed to work in a single location. If that location goes offline, then so does your entire realtime messaging capacity.

• Guarantees: Neither Socket.IO nor WebSocket offer strong messaging guarantees. Whichever of the two you choose, you’ll need to build manual functionality to track whether messages are delivered and if they’re delivered in order.

Key takeaway: Both Socket.IO and WebSocket can scale vertically to a point, but do not support out-of-the-box horizontal scaling, multi-location servers, or messaging guarantees.

Between Socket.IO and WebSocket, performance is likely to be similar using similar hardware and networks. However, worse performance from Socket.IO most likely comes in exchange for additional functionality. For example:

• Handshake: Establishing a Socket.IO connection might take marginally longer than WebSocket, as Socket.IO will always start with an HTTP connection and then attempt to upgrade to WebSocket if it is available.

• Multiplexing: The overhead of managing multiple virtual connections could add a little more processing time to the delivery of individual messages.

Realistically, though, if you implement richer functionality of your own on top of WebSocket you’ll experience a similar, albeit minimal, performance hit.

Key takeaway: The performance difference is minimal, with WebSocket coming out slightly on top for the leanest builds.

While Socket.IO and WebSocket may appear similar on the surface, we've seen that there are significant differences distinguishing the two options. Let’s look again at what sets them apart:

• Messaging library vs protocol: If you’re a NodeJS/JavaScript developer, Socket.IO gives you the tools to implement realtime messaging in your applications. WebSocket, on the other hand, is the description of a protocol for realtime communication so you will need either to select a WebSocket library or implement your own from scratch.

• Richer functionality vs customizability: Socket.IO takes care of much more than WebSocket out of the box, including multiplexing and choosing from a selection of connection methods - but the tradeoff is that it’s less customizable.

• Development overhead and maintainability: If you work within the guidelines set by Socket.IO, you're likely to get your realtime features up and running more quickly than with plain WebSocket. Another benefit is that your maintenance burden is likely to be lower as the Socket.IO community takes care of vulnerabilities, bug fixes, and new functionality. However, that comes at a cost: if you customize Socket.IO or if Socket.IO goes in a direction that causes friction with your design choices, then you might find that you have a greater maintenance burden than if you’d built your own solution with WebSocket.

In summary, as long as you are working in a JavaScript/NodeJS environment, Socket.IO gives you more functionality and a richer developer experience than a pure WebSocket library. However, there are circumstances where we recommend you choose pure WebSocket instead:

• You’re not a NodeJS developer: Although Socket.IO has community supported implementations in languages other than JavaScript, it's risky to rely on a library designed for a different programming language than the one you're using for your app. Instead, consider exploring options native to your preferred tech stack, like SignalR for .NET, or a realtime platform as a service with client libraries for multiple languages.

• You need something Socket.IO can’t deliver: If you have specialized requirements, you might be better off building with WebSocket. For example, in extremely latency sensitive scenarios such as high frequency trading, the additional overhead introduced by Socket.IO might be unacceptable. Similarly, if you need a custom message format, it might be more efficient to build with WebSocket rather than to bend Socket.IO into shape.

But it’s not a binary choice between Socket.IO and WebSocket. Let’s take a brief look at some of the other options you might consider.

There’s much more to realtime than Socket.IO vs WebSocket. Although both can be good options, they lack guarantees like message ordering and data integrity, resilience, and straightforward scaling. Just as importantly, they offer only a partial solution that leaves you with the planning and maintenance of the infrastructure needed to deliver your realtime features. So, depending on your project’s needs, it could be worth considering a different solution.

Let’s look at some of the alternatives to Socket.IO and WebSocket.

• Use a protocol’s base implementation: 

  • MQTT: Designed for IoT and other situations where bandwidth is constrained.

  • WebRTC: Peer to peer protocol whose strength lies in audio and video streaming.

• Use a messaging library:

  • SignalR: Similar to Socket.IO but for the .NET ecosystem.

  • ActionCable: Part of the Ruby on Rails framework, provides a basic WebSocket implementation but without the fallbacks or other conveniences provided by other libraries.

• Use a platform as a service (PaaS):

  • Use-case specific platform: For example, if you’re building chat functionality then you might choose a dedicated chat PaaS. However, such providers tend to be limited in terms of delivery guarantees, scalability, and resilience.

  • Back-end as a service (BaaS): Services such as Firebase and Supabase offer some realtime functionality. They can be a quick way to get up and running but their realtime limitations become quickly apparent.

  • Realtime PaaS: A dedicated realtime PaaS, such as Ably, gives you both rich functionality and resilient infrastructure. One of the weaknesses of Socket.IO and standalone WebSocket is that they solve only one part of the problem, leaving you to figure out the necessary DevOps. Ably’s global edge network puts your realtime functionality close to your end users, scales up or down with demand, and ensures your messages arrive at their destination.

If you’re interested in an alternative to Socket.IO and WebSocket, here's a bit more information on Ably’s realtime PaaS. Ably gives you:

• A global edge network: Deliver low latency to your users wherever they are in the world.

• WebSocket and more: Ably chooses the appropriate protocol, such as WebSocket, Server Sent Events, and MQTT, depending on network conditions and application needs. 

• <50 ms latency: Our expert realtime DevOps engineers manage our global network to ensure low latency right across our network.

• Resilient delivery: Ably guarantees that messages arrive in order and on time.

• 99.999% uptime: Ably’s network routes around failure to ensure your application keeps on delivering.

• Elastic scaling: As demand grows, Ably scales from thousands to billions of messages.

• Works in your language: With SDKs for more than 25 languages and frameworks, integrations with common tooling, and industry leading documentation, Ably’s developer experience gives you the tools to become productive quickly.

Discover how Ably empowers developers like you to integrate global, scalable, and efficient realtime experiences in your apps with a free account.