Can I use the SDK for the Web on localhost?

Yes, absolutely!

You can create a license key in your account  https://ssl.scandit.com/licenses

Any domain name (such as www.scandit.com) can be used for testing on local/private IP addresses.

However, please be aware that as soon as you are not testing on localhost, you will need to serve your website with https. You can use solutions such as ngrok.io to test your website with https on remote devices.

Please see more info in the following FAQ article:

Do I really need to serve my site with https?