All free tools
Small, single-purpose and free to use. Nothing to install and no sign-up.
px → em
px to em calculator
Work out em sizes from px. Set the parent size, set the size you want, and read the answer.
Responsive widths
px to percentage calculator
Turn a fixed pixel width into the percentage you need for a fluid, responsive layout.
BSE64
Image to base64 encoder
Drop in an image and get the base64 string plus a ready-made img tag. Everything happens in your browser.
nth-child tester
Test any :nth-child() formula
Type 2n+1, odd, even or any expression and see exactly which elements it selects.
Is this retina?
Check your display density
Find out whether the screen you're on is HiDPI, and see the pixel ratio behind the answer.
CSS3 generator
Radius, shadows and gradients
Adjust the sliders, watch the preview, copy the rule when it looks right.
CSS layout generator
Build a page skeleton
Pick a header, sidebars and footer, then download the HTML and CSS as a starting point.