Unfortunately, JustCode and any other tool extension could not be installed to any Express edition of Visual Studio. This is because the Express editions have some restrictions on installing extensions. Actually, only extensions that are classified as Templates (or Template Wizards) and Controls are supported by Express SKUs, so all tool extensions (i.e. all extensions that differ from Templates and Controls) could not be installed to VS 2012 Express edition.
I hope this was helpful, if you have any further questions, please, do not hesitate to contact us.
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