The purpose of @model directive

The @model directive at the top of your .cshtml file serves several critical purposes:

Establishes the Link: It explicitly tells the Razor Page (the front-end .cshtml file) which C# class (your PageModel) it is associated with. Without this link, Razor Pages has no way of knowing which OnGet, OnPost, or other handler methods to look for when a request comes in for that specific .cshtml file.

Enables IntelliSense: In development environments like Visual Studio, @model is what enables IntelliSense to suggest properties and methods from your PageModel directly within your .cshtml file (e.g., if you had a public property public string Message { get; set; } in your PageModel, you could access @Model.Message in the view). Note that @model directive tells about type while @Model tells about members of the type. The members can be properties, methods etc.

Facilitates Model Binding & Handler Execution: When a request arrives for a Razor Page, the framework looks at the URL, finds the corresponding .cshtml file, and then, based on the @model directive, instantiates the associated PageModel class. It's during this process that it determines which OnGet, OnPost, OnGetAsync, OnPostAsync, etc., handler to invoke.

Missing @model directive: Without it, Razor Pages simply does not know which C# class is meant to handle the logic for specific page. It is a very common pitfall, especially when creating new pages or copying snippets! If backing file i.e. PageModel class file is removed then @model directive is not needed. In this case, in the front .cshtml file, you can use @functions{} block to add class, properties, methods etc.