SQL Web has the same functionality as SQL Standard and is much cheaper. However it has a restrictive licensing model that states it can only support “public and Internet accessible Web sites, Web pages, Web Applications and Web services”.

It may not be used to support line of business applications (e.g., Customer Relationship Management, Enterprise Resource Management and other similar applications). 

If a website has a login it is not publicly accessible.

If any part is not publicly accessible then a SQL Standard or Enterprise Licence is required.

SQL Developer

Only SQL Web, Standard or Enterprise are available through SPLA licensing. SQL Developer edition is not, nor is it eligible for license mobility.

Therefore it can only be installed on a dedicated server, or a virtual machine that is hosted on your own dedicated server.

SQL Express

Customers are free to implement SQL Express in virtual or dedicated environments subject to the Microsoft EULA.