Zero-setup replacement for var_dump(), print_r(), and debug_backtrace().

Improving Kint

Contributor guidelines

You can see a full list of contributor guidelines in the repository. The short (And possibly out of date) version is here:

  • The code has to work from PHP 5.1.2 up to nightly, as well as the latest HHVM and HHVM nightly
  • Don’t write bad code
  • Don’t break BC
  • If you make changes make sure you run the formatter and rebuild
  • Default plugins should only handle PHP functionality
  • Don’t display incorrect information
  • Arrays may contain references. Objects are always references. Don’t alter user input in the parser.

Setting up a dev environment

For developing on core Kint you’ll need three things:

  1. Composer (PHP)
  2. Npm (NodeJS)
  3. Bundler (Ruby)

If you don’t have composer do yourself a favor and learn it. If you don’t have npm or bundler that’s understandable.

In any case, Kint uses composer, npm, and bundler for development tools. Composer calls npm and bundler under the assumption that they’re in your $PATH.

If all of these are installed simply run composer install and all your dependencies will be installed automatically.

Format and Build

The reason you need composer, npm, and bundler is because they’ll let us write sloppy code and have the computer fix it for us!

Specifically, composer runs php-cs-fixer to reformat PHP code to a consistent style, while npm and bundler do the same for the JS and CSS files.

Since code style is a good thing you should always run composer format before a commit to fix any poor code style. If you don’t CI will complain.

Since we deliver the compiled JS/CSS files in our repo you should always run composer build before a commit to rebuild the JS/CSS files. If you don’t CI will complain.

A word on JS

In JS we’re using eslint to format our code, but unlike php-cs-fixer it doesn’t always fix the code for you. Sometimes it will just complain loudly. If that happens you’ll have to read the errors and fix them by hand.

Kint architecture and design

Kint’s architecture can roughly be split into:

  • Parsing
  • Rendering
  • The Kint helper that glues them together


The Kint_Parser class is instantiated and loaded up with Kint_Parser_Plugin objects and let loose on the incoming data. It returns a Kint_Object containing information about the input data’s type, name, visibility, access path, and a list of Kint_Object_Representations of the data. (Among other things)

When it’s done parsing it loads up all the applicable Kint_Parser_Plugin and lets them alter the Kint_Object at will. By the time the object gets back it will likely have even more representations of data. Each of the representations may in turn hold more Kint_Object.

In addition to altering the Kint_Object, the plugins may add to the hints arrays on both the Kint_Object and the Kint_Object_Representation to inform the renderer as to their options.

Kint_Object can be extended to alter behavior at the object level. Again this is mostly of use in the rendering stage.


After you have a Kint_Object representing the variable, you need to render it. What the renderer does is somewhat irrelevant. It could print out text or it could print out HTML. It could store the dumped data in a database or email it to the ISS.

If you’re using the parser on it’s own you can do whatever you want with the data, but if you want to make a renderer that’s easily integrated into Kint you’ll want to extend the Kint_Renderer class.

Implementing it is fairly simple: It has three methods that return strings to output.

  • preRender()
  • render(Kint_Object)
  • postRender()

Additionally, it has an optional parserPlugins(array) method that lets the renderer alter the list of parser plugins before parsing. This lets renderers that can’t support plugins anyway disable them for performance.

The renderer typically uses text hints stored in the $object->hints and $representation->hints arrays by the parser and its plugins to inform its rendering behavior. For example, the blacklist hint causes the rich renderer to draw a crossed out button instead of a +.

The Kint helper

The Kint class is a helper for dumping data. As you’ve read above, the process for a standard Kint dump goes like this:

  • Create a renderer with state information (Calling file/line number, modifiers, parameter names, etc)
  • Call the renderer’s preRender method and echo the output
  • Create a parser
  • Add all the plugins you want to use to the parser
  • For each variable you want to dump
    • Pass it into the parser
    • Pass the parser’s output Kint_Object to the renderer and echo the output
  • Call the renderers postRender method and echo the output

This is a big list, and really painful to do on your own. The Kint class handles all of this for you. Most general options live in the Kint class, and the Kint class has only static properties and methods.

The Kint class also uses Kint_SourceParser to gather information about the calling code such as parameter names and modifiers.

Writing plugins »