Iis Express Application Compatibility Database ((new)) -

For critical legacy apps, test on a real IIS VM in addition to using IIS Express compatibility mode.

Manages compatibility for 64-bit processes, often working in tandem with the IIS Database Manager to coordinate local and remote database connections. How the Compatibility Database Works iis express application compatibility database

%ProgramFiles%\IIS Express\config\templates\PersonalWebServer\applicationhost.config (The compatibility rules are embedded in the IIS Express binary or referenced via internal DLLs like iisappcompat.dll .) For critical legacy apps, test on a real

When the database is configured correctly, it is magic. For critical legacy apps

Using Clr2ClassicAppPool vs Clr4IntegratedAppPool also triggers different compatibility rules.