Make it so that the code can not be altered, just viewed

White background hurt my eyes. Only keywords coloring is not enough for code coloring.

If you move the cursor to the opening tag highlight the closer tag

when we write a code also we need to debug , it is useful to resolve issue very fast.

It would be nice to have a user page that lists the Fiddles that we have created. A main page of sorts.

Mobile/Desktop versions switch button is needed on main menu.

Provide a method to store environment variables per our account that couldn't be seen by anyone we shared the code with.

Make them accessible in code with this: https://docs.microsoft.com/en-us/dotnet/api/system.environment.getenvironmentvariable.

Curley braces autocompletion would be so nice
and shortcut like cw + tab to write Console.WriteLine()

It would be cool to mark some words as code and others as emphasized.

some class libraries loaded from nuget need setting assembly attributes located in assemplyInfo.cs otherwise it fire an exception, like:

[assembly: AssemblyCompany("Company xyz")]

[assembly: AssemblyCopyright("Copyright © 2018 Company xyz")]

Enable setting these attributes in assemplyInfo.cs

Tidy Up is great function but I've noticed that if I'm working on a Saved code and I hit that button, the code formats and then my save button disappears..

Add support for collapsible regions

With postsharp AOP is available for C#. I wanted to try out a sample code at postharp. I downloaded the nuget package, but it didn't work.

PostSharp extends the C# and VB languages with a notion of pattern. The result: shorter, cleaner code that’s easier to write and understand, contains fewer defects and is less expensive to maintain.

Why would you make a Nuget Header Directive available for C# but not for VB.Net?

why we cant just add our <script src="xyz"> ourselves. Why adding our own css style and javascript in above our html panel doesnt work?

Please create My Fiddles on the left hand side Option's window or on right hand side (New window) so that one can easily switch between files if required.