https://jakearchibald.github.io/svgomg/

SVG files, especially exported from various editors, usually contain a lot of redundant and useless information such as editor metadata, comments, hidden elements, default or non-optimal values and other stuff that can be safely removed or converted without affecting SVG rendering result.
Source

https://webaim.org/resources/contrastchecker/

Color is an important asset in design of Web content, enhancing its aesthetic appeal, its usability, and its accessibility. However, some users have difficulty perceiving color. People with partial sight often experience limited color vision, and many older users do not see color well. In addition, people using text-only, limited-color or monochrome displays and browsers will be unable to access information that is presented only in color.
Source

https://developers.facebook.com/tools/debug/sharing/

You can use the Sharing Debugger to see the information that is used when your website content is shared on Facebook, Messenger and other places.Source

https://regexr.com/

RegExr is an online tool to learn, build, & test Regular Expressions (RegEx / RegExp). Created by the nice people at gskinner.com.Source

http://svg.enshrined.co.uk/

Contrary to what many people believe, SVG is not an image format. It is a document format. Unfortunately for us who just want vector graphics on the web, it is also quite a powerful and flexible document format. As an example, SVG files allows JavaScript to be embedded and SVG readers, i.e. your browser, are expected to execute it.Source