Can I use
Online toolCompatibility tables for web features (HTML, CSS, JavaScript) across browsers and versions.
Free, with trade-offsWebDeveloper tools4 resources
Encoding, regular expressions, browser support: everyday developer tools.
CyberChef
Online toolA web “Swiss army knife” to encode, decode, convert, encrypt and analyse data step by step; processing happens in the browser.
Completely freeWebJSFiddle
Online toolOnline playground to write and test HTML, CSS and JavaScript snippets and share them by link; funded by advertising.
Free, with trade-offsWeb
regex101
Online toolOnline regular expression tester and debugger with explanations, for many languages (PCRE, JavaScript, Python…).
Limited free planWeb