Here is a collection of tools I’ve found useful.
Performance
- Google PageSpeed Insights: pagespeed.web.dev
- GTmetrix: gtmetrix.com
- WebPageTest: webpagetest.org (Useful for waterfall chart and list of all loaded files)
Social
- Preview Open Graph data for any page: omgimg.co/social/preview
Images
- Convert SVG to CSS: yoksel.github.io/url-encoder
Plugin development
- Check to make sure your plugin actually works with the minimum WP version it declares: https://github.com/eduardovillao/wp-since