Kilian Valkhof

Building tools that make developers awesome.

Supercharging <input type=number>

Javascript, 11 August 2020

The number input type provides a nice way for to deal with numbers. You can set bounds with the min and max attributes and users can press up and down to go add or remove 1, or if you add the step attribute, go up or down by a step. But what if we want to let the user go up or down with different step sizes?

Responsive design in 2020: Recording of my Halfstack Conference talk

CSS & HTML, 22 June 2020

At Halfstack Conf in May I gave a presentation on what I think responsive design should be about in 2020 and what it will be about going forward: responding not just to static device properties like width and height but also to user preferences like preferring dark mode or reduced motion. The recording of it is out now, check it here:

The complete guide to CSS Media Queries

CSS & HTML, 15 June 2020

Media queries are what make modern responsive design possible. With them you can set different styling based on things like a users screen size, device capabilities or user preferences. But how do they work, which ones are there and which ones should you use?

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.

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.