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If you need an API key, sign up here. WebSockets are reliable, well established and easily accessible - natively supported both in-browser (JavaScript) and server-side, with libraries and example code available in most programming languages. WebSockets

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Table of Contents

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Fundamentals

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Basic Flow - Connect, Auth, Subscribe

  1. Connect to wss://fastforex.wsdx.io (and receive a connect message from the server)
  2. Send an auth message with your API key (get a free API key here)
  3. Send a subscribe message with the desired FX pairs

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JSON Message Format & Examples

Messages are sent and received in JSON format. All messages have an op field, which indicates the operation type. Messages from the server (“downstream”) will usually contain
  • a status field, which indicates the success or failure of the operation.
  • We follow HTTP status codes for this. e.g. 200 = success, 401 = not authenticated, etc.
  • a tsp field which indicates the timestamp of the message in milliseconds since epoch (Unix time).

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Upstream (sent to the WebSocket server)

Auth 
{
  "op":"auth",
  "key":"your-api-key-here"
}
Subscribe 
{
  "op": "subscribe",
  "stream": "fx",
  "pairs": ["EURUSD", "GBPUSD"]
}

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Downstream

Connect (sent by server on connect) 
{
  "op": "connect",
  "status": 200,
  "tsp": 1745877646598,
  "msg": "Connected to server"
}
Auth Response 
{
  "op": "auth",
  "status": 200,
  "tsp": 1745877646598,
  "msg": "Authenticated OK"
}
Subscribe Response 
{
  "op": "subscribe",
  "status": 200,
  "tsp": 1745877671164,
  "msg": "Subscribed to 2 streams"
}
Price 
{
  "op": "price",
  "sym": "EURUSD",
  "bid": "1.14218",
  "ask": "1.14218"
}

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Limitations, Message Volumes

Depending on your subscription plan, you may be limited on the number of concurrent WebSocket connections you can make, and to the maximum number of pairs per connect. Our standard offering allows for 2 connections and up to 5 pairs per connection. Contact us for higher limits.
Warning - High Message Volume Popular pairs such as EURUSD can generate a lot of messages at peak times - up to hundreds of messages per second. Your application should be able to handle this. Connections may be closed if you cannot consume at the publish rate. Depending on your application needs, when sending your subscribe message, you can choose to use the fx1s stream, which will produce at most one message per second, per subscribed pair.

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Examples, Demos, Code Snippets & Client Libraries

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WebSocket Playground

WebSocket King is a great in-browser tool for testing WebSocket connections. You’ll need the following information and example payloads to get started:
FieldValue
Serverwss://fastforex.wsdx.io
Auth{"op":"auth", "key":"YOUR-API-KEY-HERE"}
Subscribe{"op":"subscribe", "stream":"fx", "pairs":["EURUSD", "GBPUSD"]}

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JSFiddle (JavaScript) Example

A really simple in-browser, native JavaScript example of connecting to the WebSocket server, authenticating and subscribing to a stream. https://jsfiddle.net/ycquz7px/