Resources

Tools

Interactive tools that run in your browser. Use them alongside the lessons, in lab, or to check your own work.

URL Explorer
Break a URL into its parts and see who reads each one, take a domain apart down to its public suffix, compare two URLs for same origin and same site, and resolve relative references. Works offline.
Who is visiting?
Meet a plausible visitor to your site, with their device, network, language and access needs, and see what your page owes them rung by rung. Estimate how long your page takes them to load.