Steps to replicate the issue (include links if applicable):

Try to save this code on mobile

<templatedata>
{
	"params": {
             "1": {
			"required": false,
			"type": "string",
			"description": "Nazwa przycisku"
		}, 
    },
	"description": "Szablon dodaje przycisk do dodawania nowej sekcji"
}
</templatedata>

The param has dangling comma wich is syntax error in JSON.

What happens?:

can't save. The page is frozen on a preview page

What should have happened instead?:
There should be some kind of error indicator.

Software version (on Special:Version page; skip for WMF-hosted wikis like Wikipedia): polish Wikipedia

Other information (browser name/version, screenshots, etc.):

I was creating documentation for the template and copy pasted the JSON from docs that had two params.