Kilian Valkhof

Kilian Valkhof is a Dutch front-end developer and user-experience designer best known as the creator of Polypane, a Chromium-based browser built specifically for web developers and designers. Polypane is a one-person business: Valkhof is its founder, developer, designer and support team.

Valkhof's self-description is a user experience developer and a generalist who also handles back-end work, visual design, marketing and devops because all of it shapes a user's experience. Before Polypane, Valkhof built a range of tools for people who make websites, and writes regularly on kilianvalkhof.com about design tools, CSS and accessibility.

He announced Polypane in 2017 as a browser for a responsive development workflow: instead of resizing one window, it shows a site in many synchronized viewports side by side, with scrolling, clicking and typing mirrored across all of them. After a public beta, Polypane 1.0 launched in 2019 as a paid, cross-platform app for macOS, Windows and Linux, built on Electron. It has since added accessibility auditing, emulation of user preferences such as dark mode and reduced motion, visual debugging tools and many developer tools that ordinary browsers lack.

The software company Firstversionist, Valkhof's professional home, also publishes Superposition, which extracts a site's design tokens for use in code and design tools; Valkhof also runs FixA11y, a project that improves accessibility through tooling and education. Valkhof is a member of the Electron governance team and speaks at web conferences.

Polypane is a long-running example of a bootstrapped, single-founder developer tool that competes with free browsers by going deep on one audience.