A chrome extension and external server supporting external invocation of chome API calls.
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extension Ping handling, error checking. Nov 23, 2012
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This project has now been superseded by chromix-too. If you're a new user (or an existing user who's willing to make the switch), then I suggest that you consider using chromix-too instead.


Chromi is a Chrome extension that facilitates command-line and scripted control of Chrome through Chrome's extension API. Chromi does not include a server or a client, so it does very little on its own. A server and client are available in the Chromix project.

Who Might Want to Use Chromi?

...anyone who wants command-line or scripted access to Chrome's extension API from outside of Chrome itself. For example, Chromi allows clients to ask Chrome to load, focus or reload a tab, remove tabs, or extract Chrome's bookmarks -- all from outside of Chrome itself.

Here's an example from Chromix:

chromix with http://www.bbc.co.uk/news/ reload
chromix with http://www.bbc.co.uk/news/ focus

Reload the BBC News tab, and focus it.

Only the Chromi extension is included in this project. The client and server are available from the Chromix project.

Security Warning ...

Chromi opens a TCP socket to a server on localhost. Malicious software with access to that socket may gain unintended access to Chrome's extension APIs.

New! (21/11/2012)

The Chromi extension is now available on the Chrome Web Store.

New! (4/3/2012)

There's nothing new! This is just a quick note to say...

Despite there having been no updates recently, this project is very much alive. The hard work is all done in chromix, outside of the extension itself. So there has been little (well, almost no) need to update the extension itself.



The Chrome security model limits how extensions interact with the host operating system, and vice versa. This makes it difficult to control Chrome from the command line or via scripts.

Chromi overcomes these limitations through the use of a web socket. Specifically, Chromi uses the following architecture:

  • Client <--> Server (ws://localhost:7441) <--> Chromi (within Chrome)
    (where <--> indicates a web socket connection).

The Chromi extension connects to a web socket server on localhost:7441. Clients connecting to that same socket can then send messages to the extension and receive responses.

Client's have access to all of the callback-based operations exported by the Chrome API. Event-based callbacks are not currently supported.


When Chromi receives a suitably-formatted message, it executes the requested Chrome API function and bounces the response back to the server (and hence also to the original client).

The extension accepts text messages with four space-separated fields:

  1. the literal word chromi,
  2. an identifier (which must match the regexp /^\d+$/),
  3. the path to a Chrome JavaScript function (such as chrome.windows.getAll), and
  4. a URI encoded, JSON stringified list of arguments.

The extension calls the indicated function with the given arguments and responds with a message of the form:

  1. the literal word Chromi (note the capital "C", this time),
  2. the identifier provided with the original request,
  3. the literal word done (or error, in the event of failure), and
  4. a URI encoded, JSON stringified list of results from the function's invocation.

Chromi is a work in progress: so that's the extent of the documentation for the moment. Except for the following examples, ...


Client to Server

Here's an example of an on-the-wire client request:

chromi 137294406 chrome.tabs.update %5B86%2C%7B%22selected%22%3Atrue%7D%5D

which, when URI decoded, reads:

chromi 137294406 chrome.tabs.update [86,{"selected":true}]

The client is requesting that Chrome focus tab number 86. It may have learned this tab identifier via an earlier call to chrome.windows.getAll.

Notice that chrome.tabs.update accepts three arguments: tabId, updateProperties and callback. In this example, just the first two have been provided. Chromi itself provides the callback, and that callback arranges to broadcast the response.

This is the general approach to using Chromi: the caller must provide all arguments up to just before the callback, and Chromi adds the callback.

Server to Client

The corresponding response from the extension is:

Chromi 137294406 done %5B%7B%22active%22%3Atrue%2C%22favIconUrl%22%3A%22http%3A%2F%2Fwww.met.ie%2Ffavicon.ico%22%2C%22highlighted%22%3Atrue%2C%22id%22%3A86%2C%22incognito%22%3Afalse%2C%22index%22%3A2%2C%22pinned%22%3Afalse%2C%22selected%22%3Atrue%2C%22status%22%3A%22complete%22%2C%22title%22%3A%22Rainfall%20Radar%20-%20Met%20%C3%89ireann%20-%20The%20Irish%20Meteorological%20Service%20Online%22%2C%22url%22%3A%22http%3A%2F%2Fwww.met.ie%2Flatest%2Frainfall_radar-old.asp%22%2C%22windowId%22%3A1%7D%5D

which, when URI decoded, is:

Chromi 137294406 done [{"active":true,"favIconUrl":"http://www.met.ie/favicon.ico","highlighted":true,"id":86,"incognito":false,"index":2,"pinned":false,"selected":true,"status":"complete","title":"Rainfall Radar - Met Éireann - The Irish Meteorological Service Online","url":"http://www.met.ie/latest/rainfall_radar-old.asp","windowId":1}]

Here, the request succeeded and returned a snapshot of the tab's state. This is the data passed by chrome.tabs.update to its callback.

Dependencies and Installation

The Chromi extension is available on the Chrome Web Store.

Alternatively, the extension can be downloaded and installed as an unpacked extension directly from the project folder (see "Load unpacked extension..." on Chrome's "Extensions" page). It may be necessary to enable "Developer mode" in Chrome.

The dependencies for building Chromi include, but may not be limited to:

  • Node.js
    (Install with your favourite package manager, perhaps something like sudo apt-get install node.)

  • CoffeeScript
    (Install with something like npm install coffee-script.)

Run cake build in the project's root folder. This compiles the CoffeeScript source to JavaScript.

cake is installed by npm as part of the coffee-script package. Depending on how the install is handled, you may have to search for where npm has installed cake.


If it cannot connect to the server or if a connection fails, then Chromi attempts to reconnect once every five seconds.


  1. Allow the TCP port number to be configured via an options page.
  2. Is there a reasonable approach to securing communications?
  3. Support callbacks on Chrome events.