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WebSocket benchmark utility


Thor is WebSocket benchmarking/load generator. There are a lot of benchmarking tools for HTTP servers. You've got ab, siege, wrk and more. But all these tools only work with plain ol HTTP and have no support for WebSockets - even if they did they wouldn't be suitable, as they would be testing short running HTTP requests instead of long running HTTP requests with a lot of messaging traffic. Thor fixes all of this.

Websocket (ws)

npm run ws
thor-hammer --amount 4096 --concurrent 512 http://localhost:9090


npm run sockjs
thor-hammer --amount 4096 --concurrent 512 --transformer sockjs http://localhost:9090

npm run socketio
thor-hammer --amount 4096 --concurrent 512 --transformer socketio http://localhost:9090

Express 3 +

npm run express-socketio
thor-hammer --amount 4096 --concurrent 512 --transformer socketio http://localhost:9090

Redis +

npm run redis
npm run redis-socketio
thor-hammer --amount 4096 --concurrent 512 --transformer socketio http://localhost:9090

Primus + Websocket

npm run primus-ws
thor-hammer --amount 4096 --concurrent 512 --transformer primus-ws http://localhost:9090

Primus +

npm run primus-socketio
thor-hammer --amount 4096 --concurrent 512 --transformer primus-socketio http://localhost:9090

Primus +

npm run primus-engineio
thor-hammer --amount 4096 --concurrent 512 --transformer primus-engineio http://localhost:9090

Primus + Sockjs

npm run primus-sockjs
thor-hammer --amount 4096 --concurrent 512 --transformer primus-sockjs http://localhost:9090


Thor requires Node.js to be installed on your system. If you don't have Node.js installed you can download it from or build it from the github source repository:

Once you have Node.js installed, you can use the bundled package manager npm to install this module:

npm install -g thor

The -g command flag tells npm to install the module globally on your system.


thor [options] <urls>

Thor can hit multiple URL's at once; this is useful if you are testing your reverse proxies, load balancers or just simply multiple applications. The url that you supply to thor should be written in a WebSocket compatible format using the ws or wss protocols:

thor --amount 5000 ws://localhost:8080 wss://localhost:8081

The snippet above will open up 5000 connections against the regular ws://localhost:8080 and also 5000 connections against the secured wss://localhost:8081 server, so a total of 10000 connections will be made.

One thing to keep in mind is you probably need to bump the amount of file descriptors on your local machine if you start testing WebSockets. Set the ulimit -n on machine as high as possible. If you do not know how to do this, Google it.


  Usage: thor [options] ws://localhost
    -h, --help                      output usage information
    -A, --amount <connections>      the amount of persistent connections to generate
    -C, --concurrent <connections>  how many concurrent-connections per second
    -M, --messages <messages>       messages to be send per connection
    -P, --protocol <protocol>       WebSocket protocol version
    -B, --buffer <size>             size of the messages that are send
    -W, --workers <cpus>            workers to be spawned
    -G, --generator <file>          custom message generators
    -M, --masked                    send the messaged with a mask
    -b, --binary                    send binary messages instead of utf-8
    -V, --version                   output the version number

Some small notes about the options:

  • --protocol is the protocol version number. If you want to use the HyBi drafts 07-12 use 8 as argument or if you want to use the HyBi drafts 13-17 drafts which are the default version use 13.
  • --buffer should be size of the message in bytes.
  • --workers as Node.js is single threaded this sets the amount of sub processes to handle all the heavy lifting.

Custom messages

Some WebSocket servers have their own custom messaging protocol. In order to work with those servers we introduced a concept called generators a generator is a small JavaScript file that can output utf8 and binary messages. It uses a really simple generator by default.

Checkout for an example of a generator.

thor --amount 1000 --generator <file.js> ws://localhost:8080


thor --amount 1000 --messages 100 ws://localhost:8080

This will hit the WebSocket server that runs on localhost:8080 with 1000 connections and sends 100 messages over each established connection. Once thor is done with smashing your connections it will generate a detailed report:

Thor:                                                  version: 1.0.0
God of Thunder, son of Odin and smasher of WebSockets!
Thou shall:
- Spawn 4 workers.
- Create all the concurrent/parallel connections.
- Smash 1000 connections with the mighty Mjölnir.
The answers you seek shall be yours, once I claim what is mine.
Connecting to ws://localhost:8080
  Opened 100 connections
  Opened 200 connections
  Opened 300 connections
  Opened 400 connections
  Opened 500 connections
  Opened 600 connections
  Opened 700 connections
  Opened 800 connections
  Opened 900 connections
  Opened 1000 connections
Online               15000 milliseconds
Time taken           31775 milliseconds
Connected            1000
Disconnected         0
Failed               0
Total transferred    120.46MB
Total received       120.43MB
Durations (ms):
                     min     mean     stddev  median max
Handshaking          217     5036       4094    3902 14451
Latency              0       215         104     205 701
Percentile (ms):
                      50%     66%     75%     80%     90%     95%     98%     98%    100%
Handshaking          3902    6425    8273    9141    11409   12904   13382   13945   14451
Latency              205     246     266     288     371     413     437     443     701