Friend or foe

I am your best friend or worst enemy.

You decide.

I can flow words of wisdom,

Or breed vectors of venom.

I can destroy you, or uplift you.

My back is bound to you,

But I am as loose as you will.

You can sharpen me, or silver me,

But if you are wise, you will control me.

Because you are my owner,

And I am your tongue.