Where does IntelliSense for Azure JSON templates originate from?

In an Azure JSON template Visual Studio Code alerted me of a bad value for an attribute. How does Visual Studio Code know it's an Azure Resource Manager template and where does that IntelliSense come from?

I can't imagine that's baked into Visual Studio Code itself, is it? I'd like to give feedback on a piece of IntelliSense that appears outdated, but don't know where or to whom.

I disabled all Azure extensions and it continues to provide IntelliSense. Is it pulling this from the schema URL within the JSON? I've never understood the purpose of that schema URL.

• VSCode also has built-in support for JSON Schema. It provides basic IntelliSense like auto-completion and validation based on the schema of the JSON file you're looking into.

• VSCode provides IntelliSense support for Azure JSON templates with the help of Azure Resource Manager (ARM) Tools extension.

• ARM Tools extension provided by Microsoft offers language server support for Azure Resource Manager deployment JSON templates and script files.
• It provides features like IntelliSense, syntax highlighting, code snippets to edit the ARM templates directly within the VSCode.

When you open any Azure resource related JSON template, VSCode recognizes the file extension and allow the ARM Tools extension to edit the code.

• I have opened a sample Azure related JSON template in my VSCode, could see it automatically starting the Language Server to analyze the scchema.

• Check if the Azure Resource Manager (ARM) extension is installed in your VSCode.