Run your Pure Data patches on the web.
JavaScript Pure Data
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WebPd is a 100% JavaScript Pure Data runtime using Web Audio API to play audio in the browser. It aims at allowing a subset of Pure Data programming language to run in the browser without plugins and with best possible performance.

WebPd should be supported by all browsers supporting Web Audio API.

The following documentation is only about WebPd. To learn more about Pure Data, and start creating Pd patches which you can later use with WebPd, please refer to the official Pure Data documentation.

Quick start

The following instructions provide a quick start for people with JavaScript knowledge. If you have no experience with JS, you might want to read the step-by-step guide instead.

  1. Grab the latest version of WebPd from here.

  2. Add WebPd to your Web page, and load a patch by calling Pd.loadPatch.

<!doctype HTML>
    <script src="js/jquery.js"></script>
    <script src="js/webpd-latest.js"></script>
        var patch
        $.get('patches/myPatch.pd', function(patchStr) {
          patch = Pd.loadPatch(patchStr)


If you are testing locally, the ajax request might be blocked by your browser because of same-origin policy. For a workaround, see the troubleshooting section.

Step-by-step guide

The following instructions provide a detailed guide to start working with WebPd. If you have experience with web development, you might want to read the quick start instead.

  1. First create a folder myProject in which you will create your first WebPd project. In this folder, create the following structure :
  1. Download the latest version of WebPd, save it as webpd-latest.js onto your computer, in the folder myProject/js.

  2. Download the latest version of jquery, save it as jquery.js onto your computer, in the folder myProject/js.

  3. In the folder myProject, create a file called index.html and copy/paste the following code in it

<!doctype HTML>
    <script src="js/jquery.js"></script>
    <script src="js/webpd-latest.js"></script>
        var patch
        $.get('patches/myPatch.pd', function(patchStr) {
          patch = Pd.loadPatch(patchStr)


Save that file. Be sure to use a text editor that is programmer-friendly. Microsoft Word and other text processors will add a lot of extra informations, making your code impossible to understand by a web browser. I recommend using something like atom, notepad, gedit, ...

  1. Create a patch using Pure Data. Make sure that you use only features and objects supported by WebPd. Save that patch as myPatch.pd in the folder myProject/patches.

  2. Because we are working locally on our computer, we now need to run a web server to be able to open the web page index.html properly. For this, we will use the web server that comes with Python.

Chances are, you already have Python installed on your computer. To check this, open a terminal (or command prompt), and run python --version, this should print the version of Python installed. If instead you get something like command not found, then you need to install Python.

In the terminal use the command cd to navigate to the folder myProject. When you've arrived there, run the command python -m SimpleHTTPServer if you have Python 2 or python -m http.server if you have Python 3.

  1. You can finally open your web page and listen to your patch, by opening a web browser and navigating to http://localhost:8000/index.html.

  2. Next :


There are a few examples in the examples/ folder. You can also open them online :


I can't run any WebPd demo on my computer

For security reasons, browsers control access to your file system from web pages. Because of this, getting Pd files with Ajax might fail on your local machine. A workaround is to start a local server and access all the example web pages through it.

Python comes bundled with such a web server. Open a terminal, navigate to the folder containing the web page you want to open, then run python -m SimpleHTTPServer if you are using Python 2 or python -m http.server if you are using Python 3. Then open your web browser to http://localhost:8000 and things should start working.

Alternatively, if you prefer node, you may want to install the handy http-server command-line utility.

One of my patches doesn't work in WebPd

WebPd has a few limitations. For example, some of the Pd objects are not available. Open your browser's developer console (ctrl+shift+i on firefox and chrome for linux or windows), and you should get a clear error message telling you what is wrong. If the error is unclear, or if there is no error, it might be a bug with WebPd. In that case, it would be great if you could submit a bug report.

Here is a non-exhaustive list of other limitations and inconsistencies with Pure Data :

  • Pd system messages, such as the widely used [;pd dsp 1( , are not implemented
  • [phasor~] is not a real, perfect, phasor. You shouldn't use it to read from an array for example.
  • [phasor~] inlet 2 (used to set the phase) is not implemented

A patch that works fine on the desktop doesn't seem to work on mobile

WebPd uses Web Audio API, and as it happens, running Web Audio API on mobile is not always easy. First, make sure that you use a browser that does support Web Audio API. For example the default Android browser does not, and so on Android you have to use Chrome or Firefox.

On iPhone and iPad, you need to use the Pd.startOnClick helper, otherwise the sound will not work.

Also some objects such as [adc~] depend on features which are not available in all browsers and on all platforms. For example [adc~] won't work on iOS.

List of implemented objects and other limitations

Not all of Pure Data's objects are available in WebPd. Please check-out the list of available objects.

Abstractions are implemented, but at the moment they require a bit of extra JavaScript in order to work. You can check-out the abstractions example, to see how this works.

While WebPd uses only Web Audio API and should therefore be quite efficient, you might find that some patches perform poorly on mobile devices, or if there are too many objects running at the same time. This is because Web Audio API is not optimized to work in the same way as Pure Data. For example, modulating parameters with an audio signal (frequencies, delay times, ...), though it is very frequent in Pd, can cause audio glitches in the browser if you use it too much or in a big patch.

Submitting a bug report

If you find a bug, you can submit a bug report on the project's issue tracker.

Please try to include as much information as possible. Also try to include code, and the patch that you cannot get to work.


You can use WebPd API to create patches, add objects, connect them, disconnect them, etc ... with JavaScript. Something called "dynamic patching" in Pure Data. Here is a quick example :

var patch = Pd.createPatch()                  // Create an empty patch
  , osc = patch.createObject('osc~', [440])   // Create an [osc~ 440]
  , dac = patch.createObject('dac~')          // Create a [dac~]
osc.o(0).connect(dac.i(0))                    // Connect outlet of [osc~] to left inlet of [dac~]
osc.o(0).connect(dac.i(1))                    // Connect outlet of [osc~] to right inlet of [dac~]
osc.i(0).message([330])                       // Send frequency of [osc~] to 330Hz

You can also use the API to integrate WebPd with pure Web Audio code. For example :

var patch = Pd.loadPatch(patchStr)            // We assume this patch has an [outlet~] object
  , gain = Pd.getAudio().context.createGain() // We create a web audio API GainNode
patch.o(0).getOutNode().connect(gain)         // Connect the output 0 of the patch to our audio node

Below you can find a (mostly) complete documentation of the WebPd API. Please note that dynamic patching with WebPd is still experimental, so you might encounter some bugs. If you do, please report them to in the issue tracker.



Starts WebPd DSP.


Returns true is WebPd DSP is started, false otherwise.


Stops WebPd DSP.


Loads a Pd patch, and returns a Patch object. patchStr is the whole contents of a Pd file (and not only a file name).


Creates and returns an empty Patch object.


Stops and destroys patch.

Pd.receive(name, callback)

Receives messages from named senders within a patch (e.g. [send someName]). Example :

Pd.receive('someName', function(args) {
  console.log('received a message from "someName" : ', args)

Pd.send(name, args)

Sends messages from JavaScript to a named receiver within a patch (e.g. [receive someName]). Example :

Pd.send('someName', ['hello!'])


Returns the audio driver used by WebPd on the current page. the returned object has an attribute context which is an instance of Web Audio API AudioContext used by WebPd in the current page to instantiate low-level audio nodes. This can be useful to integrate WebPd with pure Web Audio code.

Pd.registerAbstraction(name, patchStr)

Registers an abstraction to WebPd. See full example there.

Pd.registerExternal(name, customWebPdObject)

Registers a custom object to WebPd. See full example there.


Get a list of audio formats supported by the current browser. For more info see web-audio-boilerplate. Example usage :

Pd.getSupportedFormats(function(supported) {

  // If ogg is supported, send a message to [receive MY-SAMPLE] with url to ogg file
  if (supported.indexOf('ogg') !== -1) {
    Pd.send('MY-SAMPLE', '/path/to/sample.ogg')

  // Otherwise if ogg not supported but mp3 is ...
  } else if (supported.indexOf('mp3') !== -1) {
    Pd.send('MY-SAMPLE', '/path/to/sample.mp3')

  } else {
    alert('this web browser is not supported, sorry!')

Pd.startOnClick(htmlElement, callback)

This is a helper to maximize browser support, especially useful for iOS. For more info see web-audio-boilerplate. Example usage :

<button id="startButton">Start patch</button>
  // Now, when user clicks on button, Pd will start and sound should work even on iOS.
  var button = document.getElementById('startButton')
  Pd.startOnClick(button, function() {


This is the base class for all WebPd nodes, patches, dsp or glue objects.


Returns the outlet ind of the node. If ind is out of range, an error will be thrown.


Returns the inlet ind of the node. If ind is out of range, an error will be thrown.


Patch.createObject(name, args)

Creates a new object of type name with arguments args. Example :

var triggerObject = patch.createObject('trigger', ['bang', 'float', 'float'])


Base class for Inlet and Outlet objects.


Connects an inlet with and outlet. If they are already connected, nothing will happen.


Disconnects an inlet and an outlet. If they are not connected, nothing will happen.



Sends a message to the inlet. args is a list of arguments. Example :


Instructions for building webpd.js

To build WebPd yourself, you will need node.js and gulp.js.

When these are installed, run npm install in WebPd root folder.

Finally, run npm run build to build a new version of WebPd in dist/webpd-latest.js.

Instructions for running the tests

WebPd comes with two test suites.

Automated tests

The tests in test/lib run on node.js using mocha. To run them, simply execute the command npm test.

Browser tests

The tests in test/browser run in a web browser.

To build them, first scaffold by running node node_modules/waatest/bin/scaffold.js ./waatest. This will create a folder waatest containing a test web page.

Build the tests by running npm run

Then start a local web server (see troubleshooting), and open waatest/index.html in your web browser.


Any kind of contribution would be very welcome. Check out the issue tracker or contact me directly.