Kilian Valkhof

Building tools that make developers awesome.

Accessibility is not like drowning

Accessibility, 21 May 2020

Accessibility is not like drowning. I mean it obviously isn’t, but let me explain why I’m comparing the two. Today is Global Accessibility Awareness Day, and there’s something I want to talk about.

Creating files in JavaScript in your browser

Javascript, 19 May 2020

Did you know you can create files using JavaScript right inside your browser and have users download them? You can create files with a proper name and mime type and it only takes a few lines of code.

For many, accessibility is an unknown unknown

Accessibility, 4 May 2020

An unknown unknown is something you don’t know you don’t know. When you’re just starting out with web development there are many unknown unknowns. You don’t know enough about what’s possible to know what the right way to do things is. Accessibility is one of them.

Your dark mode toggle is broken

CSS & HTML, Design, 27 April 2020

With more and more sites gaining support for dark mode and adding very pretty toggles to their design, it’s important to implement them correctly. Unfortunately most sites do not and as a result their toggle is broken.

New online tools: CSS specificity calculator and color contrast checker

CSS & HTML, 30 March 2020

My goal with Polypane is improving the workflow for developers and designers. The main focus is of course developing an excellent browser for developers and designers, but I’m also developing online tools that help out during development. Two of them online now are a CSS specificity calculator, and a color contrast checker. Both of them go way beyond what you expect from these types of tools.

Polypane browser for responsive web development and design Hi, I'm Kilian. I make Polypane, the browser for responsive web development and design. If you're reading this site, that's probably interesting to you. Try it out!

I develop more software and tools:


Use the design system you already have


A cross-platform, simple and smart autosaving scratchpad.

A Messenger Adventure!

Go on a text adventure in Facebook Messenger.


The latest Electron news, articles, apps and interviews.


Drag-and-drop lossless compression of PNG and JPG images for web.

Messenger Demo Viewer

Demo your (bot) interactions on Messenger.