Per the question here,
What's "tools:context" in Android layout files?
The \'tools\' namespace reference (xmlns:tools=\"http://schemas.android.
Think of them as design time helpers only.They do not get processed in actual view rendering at run time.
For example you want to set background of some view in your layout design when working on android studio so that you can make clear distinction where that particular view is.So you would normally do that with
android:background="@color/"
Now risk is that sometimes we forget to remove that color and it gets shipped in apk. instead you can do as follows:
tools:background="@color/"
These changes will be local to android studio and will never get transferred to apk.
And also check out http://tools.android.com/tech-docs/tools-attributes for more options.