Responsize

See your app the way every user sees it

Every screen, every user setting, every version of your code. A free and open source desktop app for you and your AI agent, in preparation

Follow the project

Checking an app is slow, and your AI agent cannot do it

If you code by hand

  • To test dark mode, reduced motion or another language, you change your system settings, then change them back
  • You resize the browser again and again to test each screen size
  • You find an accessibility problem or a page that is too big and slow only after it is online
  • When the layout breaks, you search for the commit that broke it

If an AI agent codes for you

  • The agent writes code, but it cannot see the result
  • It says "done" without checking on mobile, in dark mode or in another language
  • It cannot prove that the change did not break something else
  • So you check everything again yourself

Responsize will give you and your agent the same view and the same checks. Your agent will use every feature below through MCP (Model Context Protocol)

Planned features

Every user setting

Dark or light mode, reduced motion, high contrast, another language, right to left, zoom, color blindness, slow network: test them all without changing your system settings

Every screen at once

Click and use your real app at many screen sizes side by side, even sizes bigger than your own screen

Every version

A small git client shows your app at any commit or tag, compares two versions and helps you find the commit that broke something

Checks on every build

Each build checks accessibility, eco-design, HTML and CSS, browser errors and broken links, and Lighthouse scores, then compares the results with another commit

Your build, found and run

Responsize reads your config (package.json, GitLab CI, GitHub or Forgejo workflows, Vercel, Netlify, Dockerfile), builds your project and builds it again each time you change a file

Screenshots in device frames

Take screenshots at several sizes, in phone, tablet and laptop frames, for a client or for your docs

Back after more than ten years

In 2014, Silex Labs made Responsize, a small tool to show a website at other screen sizes. Now it is coming back as a desktop app that will show much more than screen sizes

In the works

Responsize is not ready yet: the project is at the planning stage and there is nothing to download. Follow it and say what you need: your ideas will help decide what goes in the app

Share your ideas on the forum