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Helps front-end developers to reach a good quality and good performances, based on phantomas and grunt-phantomas.
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This project is not maintained anymore. Please have a look at Yellow Lab Tools and grunt-yellowlabtools for replacements.

Helps front-end developers to reach a good quality and good performances, based on phantomas and grunt-phantomas.

Day after day, while working on your project, keep an eye on performance metrics and get warnings for things you should optimize.

Dependency Status

Install method 1: i don't care about Grunt

Use this minimalist installation if you just want to launch some quick tests.

You need NodeJS v0.8 or higher. If you don't have it, go to and grab the latest version.

  1. Create a directory for your grunt-devperf installation, anywhere you want. Let's call it devperf:
mkdir devperf
cd devperf
  1. Install Grunt globally:
npm install grunt-cli -g
  1. Install grunt-devperf locally:
npm install grunt-devperf
  1. Copy the example Gruntfile.js to the root of your devperf directory:
cp node_modules/grunt-devperf/demo/smallest-config/Gruntfile.js ./
  1. Then edit this copy of Gruntfile.js to insert your own list of URLs.

It's done! You can launch your first test with this command:


Install method 2: i already love Grunt

This plugin requires Grunt ~0.4.4.

Install the plugin:

npm install grunt-devperf --save-dev

Once the plugin has been installed, it may be enabled inside your Gruntfile with this line of JavaScript:


I recommand using it as a part of your Continuous Integration system, but you can also simply use it locally while developping.

Setup the "devperf" task


In your project's Gruntfile, add a section named devperf to the data object passed into grunt.initConfig().

  devperf: {
    options: {
      urls: [



Type: Array of Strings Default value: ['']

The list of URLs you want to test. Don't forget the protocol (http:// or https://), even on localhost.


Type: Integer Default value: 5

The number of times you want phantomas to call each page. A higher number of runs could give a better accuracy, but note that they are run in parallel and that your machine's bandwith may suffer.


Type: Integer Default value: 120

The time after which phantomas should cancel a run.


Type: Boolean Default value: false

Automatically opens the browser on the results page when the devperf task is finished.


Type: String Default value: ./devperf

This is the folder where the results will be generated, including grunt-phantomas reports. It can be relative to your project: ./my-folder (you might want to add this folder to your .gitignore file). Or it can be anywhere else in your file system: /var/www/devperf

Usage Examples

In this example, several Urls are tested

  devperf: {
    options: {
      urls: [
      numberOfRuns: 5,
      timeout: 120,
      openResults: true,
      resultsFolder: './devperf'

Then, open the index.html file with your browser to see the results. It is located in the results folder (./devperf/by default).

Results snapshot: grunt-devperf example results

About the results:

  • Yes it looks like a console but it's a web page!
  • Some metrics might have decimals, because they are averages of multiple runs.
  • The link to the grunt-phantomas report will give you tons of details, very helpful for debugging.
  • The files size are not reliable (sometimes gzipped, sometimes not). Check issue #6.

Warnings list

Default list of warnings

When a metric is greater than the limit, the message is displayed.

Metric Limit Message
requests 200 Too many requests, i guess your site is slow, isn't it?
cssCount 6 Too many CSS files, use concatenation
jsCount 12 Too many JS files, use concatenation
imageCount 30 Too many images, use lazyloading
smallImages 20 Too many small images (<2kB), build sprites
imageSize 512000 Total image size (bytes) is too high, try image optimisation
webfontCount 4 Too many custom fonts, tell the designer you don't want that
notFound 0 Number of 404 errors
multipleRequests 1 Some static assets are requested multiple times
imagesWithoutDimensions 5 Number of images without dimensions
commentsSize 1000 Reduce size of comments in HTML
whiteSpacesSize 8000 Reduce the number of whitespaces in HTML
DOMelementsCount 2000 Reduce the number of DOM elements
documentWriteCalls 0 Remove all document.write() calls
jsErrors 0 Number of Javascript errors
consoleMessages 0 Remove console.log or console.whatever
DOMqueries 200 Reduce number of DOM queries
DOMqueriesDuplicated 30 Many duplicated DOM queries, try to save results into variables
DOMinserts 100 Reduce number of DOM insertions
jQuerySizzleCalls 300 Reduce number of Sizzle calls (= jQuery DOM queries)
headersSentSize 20000 Reduce size of headers sent (cookies?)

Modifying the warnings

In the Gruntfile, you can change any of them by adding a warnings option this way:

  devperf: {
    options: {
      urls: [
      warnings: [
          // Changing the limit for this variable
          variable : "jsErrors",
          limit : 42,
          // Changing the message
          variable : "jQuerySizzleCalls",
          message : "I like this message best"
          // Changing the limit and the message
          variable : "DOMelementsCount",
          limit : 200,
          message: "DOM elements number is my big issue so i reduced the limit"
          // Disabling a warning (-1 is infinite)
          variable : "consoleMessages",
          limit : -1
          // Adding one of the numerous Phantomas variables not handled by grunt-devperf
          variable : "jsonCount",
          limit : 5,
          message : "I really care about having a small number of JSON requests"

You can find the complete list of Phantomas variables and their descriptions here. If you think one of these variables deserves a warning in grunt-devperf, don't hesitate to open an issue!

Advanced Phantomas options


Type: Object Default value: {}

Use this if you need to send parameters to phantomas. You can find the list of parameters here. You can enable some features such as proxy, authentification or domain blocking.


  devperf: {
    options: {
      urls: [
      phantomasOptions: {
        'proxy': 'localhost:8080',
        'no-externals': true


This project is in early stage (beta). You can help by reporting any issue, giving your feedback or coding new functionnalities.


  • Write tests
  • Create profiles for phones and tablets (force viewport and UA, decrease some of the limits)


Gaël Métais. I'm a webperf freelance based in Paris. I can also help your company about Web Performances, visit my website.