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 The short (And possibly out of date) version is here: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 5.3 up to 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 builtin 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 two things:

  1. Composer (PHP)
  2. Npm (NodeJS)

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

In any case, Kint uses composer and npm for development tools. Composer calls npm 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, and npm 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 does the same for the JS and SASS 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.

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\BasicObject containing information about the input data’s type, name, visibility, access path, and a list of Kint\Object\Representation\Representation of the data. (Among other things)

When it’s done parsing it loads up all the applicable plugins and lets them alter the 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 objects.

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

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


After you have an object 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\Renderer class.

Implementing it is fairly simple: It has 4 methods that return strings to output.

  • preRender()
  • render(BasicObject)
  • renderNothing()
  • postRender()

Additionally, it has an optional filterParserPlugins(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 hints 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\Kint class is a helper for dumping data. The process for a standard Kint dump goes like this:

  • Get the settings for this dump.
    • Static settings on the Kint class
    • Information from the backtrace
    • Information from the call site
      • Variable names
      • Modifiers
  • Create a parser and set it up
  • Add all the plugins you want to use to the parser
  • Create a renderer and set it up
  • Call the renderer’s preRender method and echo the output
  • For each variable you want to dump
    • Pass it into the parser
    • Pass the parser’s output object to the renderer and echo the output
  • Call the renderers postRender method and echo the output

Some of the generic options are handled by Kint\Utils, and information about the call site is handled by Kint\CallFinder. The facade that ties it all together

Writing plugins »