0.13.0-1 • Public • Published
`µWS` is one of the most lightweight, efficient & scalable WebSocket & HTTP server implementations available. It features an easy-to-use, fully async object-oriented interface and scales to millions of connections using only a fraction of memory compared to the competition. While performance and scalability are two of our top priorities, we consider security, stability and standards compliance paramount. License is zlib/libpng (very permissive & suits commercial applications).
  • Autobahn tests all pass.
  • One million WebSockets require ~122mb of user space memory (112 bytes per WebSocket).
  • By far one of the fastest in both HTTP and WebSocket throughput (see table below).
  • Linux, OS X, Windows & Node.js support.
  • Runs with raw epoll, libuv or ASIO (C++17-ready).
  • Valgrind & AddressSanitizer clean.
  • Permessage-deflate, SSL/TLS support & integrates with foreign HTTP(S) servers.
  • Multi-core friendly.

Simple & modern

The interface has been designed for simplicity and only requires you to write a few lines of code to get a working server:

#include <uWS/uWS.h>

int main() {
    uWS::Hub h;

    h.onMessage([](uWS::WebSocket<uWS::SERVER> ws, char *message, size_t length, uWS::OpCode opCode) {
        ws.send(message, length, opCode);

    h.onHttpRequest([](uWS::HttpResponse *res, uWS::HttpRequest req, char *data, size_t length, size_t remainingBytes) {
        res->end(const char *, size_t);


Get the sources of the uws.chat server here. Learn from the tests here.

Widely adopted

Not your average server

µWS was designed to perform well across the board, not just in one specific dimension. With excellent memory usage paired with high throughput it outscales Socket.IO by 180x.

Benchmarks are run with default settings in all libraries, except for ws which is run with the native performance addons. Read more about the benchmarks here.

Getting started


First of all you need to install the required dependencies. This is very easily done with a good open source package manager like Homebrew for OS X, vcpkg for Windows or your native Linux package manager.

Always required:

  • OpenSSL 1.0.x
  • zlib 1.x

Not required on Linux systems:

  • libuv 1.3+
  • Boost.Asio 1.x

On Linux systems you don't necessarily need any third party event-loop library, but can run directly on the high performance epoll backend (this gives by far the best performance and memory usage). Non-Linux systems will automatically fall back to libuv.

If you wish to integrate with a specific event-loop you can define USE_ASIO or USE_LIBUV as a global compilation flag and then link to respective libraries.


Clone and enter the repo:

  • git clone https://github.com/uWebSockets/uWebSockets.git && cd uWebSockets
OS X & Linux

Compile with Make:

  • make
  • sudo make install

Compile with Visual C++ Community Edition 2015 or later. This workflow requires previous usage of vcpkg:

  • Open the VC++ project file
  • Click Build

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npm i @hola.org/uws

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  • hola.org